bastion 0.57.0

client-go/anchor.go

@@ -574,9 +574,10 @@ var allCaps = []string{"dcn", "egress", "harness", "inference", "models", "obser
 // writes a pairing PENDING when an anchor exists (pair.go), and state "" reads
 // active (config.go), so B comes straight up with full lanes.
 //
-// LOCAL is exempt and must stay so: a local bastion serves one host and cannot
-// be anchored at all (cmdClaimAnchor refuses outside networked mode), so the
-// pairing IS the authorization there. Most bastions are local.
+// LOCAL is exempt and must stay so: a local bastion serves the one host it was
+// paired with, and a second only on a yes typed at the machine (pair_terminal.go),
+// and it cannot be anchored at all (cmdClaimAnchor refuses outside networked
+// mode), so the pairing IS the authorization there. Most bastions are local.
 //
 // self-update is deliberately INSIDE the refusal. Directing a binary swap is the
 // most dangerous thing on the list, and an unanchored networked box cannot say
@@ -1033,7 +1034,7 @@ func cmdClaimAnchor(token string, rotate bool, owner, host string) error {
 		return err
 	}
 	if boxMode() != modeNetworked {
-		return fmt.Errorf("claim-anchor needs networked mode — a local bastion serves one host and needs no anchor (%s, then `privatae-bastion set-mode networked`)", adminHowTo())
+		return fmt.Errorf("claim-anchor needs networked mode — a local bastion serves only the Hosts its person said yes to and needs no anchor (%s, then `privatae-bastion set-mode networked`)", adminHowTo())
 	}
 	cfgs, err := loadPairings()
 	if err != nil {

client-go/coders.go

@@ -1229,10 +1229,17 @@ func coderContainerGone(rt, cname string) bool {
 // anchor pairing on an anchored box (serviceOwnerRefusal's rule).
 // An unknown owner proves nothing about self, so it gets the anchor-only rule
 // too: every run this bastion starts records and labels its owner.
+//
+// A local machine has no anchor, so anchorOnly lets every pairing through
+// there; once it serves several Hosts (localServesSeveralHosts), each stops
+// only the runs it started, as with the servers each built.
 func coderOwnerRefusal(self, owner string) string {
 	if owner != "" && owner == self {
 		return ""
 	}
+	if localServesSeveralHosts() {
+		return "refused: that run was started by " + orUnknown(owner) + "; on a local machine that serves several Hosts each stops only the runs it started"
+	}
 	if why := anchorOnly(self, "stopping a run another host started"); why != "" {
 		return "refused: that run was started by " + orUnknown(owner) + "; " + why
 	}

client-go/config.go

@@ -615,7 +615,7 @@ func removeStalePairingFile(hostName string) error {
 func checkPairConflict(cfgs []*Config, handle string, replace bool) (*Config, error) {
 	existing := pairingFor(cfgs, handle)
 	if existing != nil && !replace {
-		return nil, fmt.Errorf("already paired with %s — this daemon serves multiple hosts, so pairing never overwrites; to rotate that host's credentials run `privatae-bastion pair --replace <token>`", existing.HostName)
+		return nil, &alreadyPairedError{host: existing.HostName, msg: fmt.Sprintf("already paired with %s — this daemon serves multiple hosts, so pairing never overwrites; to rotate that host's credentials run `privatae-bastion pair --replace <token>`", existing.HostName)}
 	}
 	if existing == nil && replace {
 		return nil, fmt.Errorf("pair --replace: no existing pairing matches '%s' — pair it normally first", handle)

client-go/install_ps1_test.go

@@ -0,0 +1,56 @@
+package main
+
+import (
+	"os"
+	"os/exec"
+	"path/filepath"
+	"strings"
+	"testing"
+)
+
+// install.ps1 has no Windows runner here, so its -Pair shape is read from the
+// file: the code is checked before anything is downloaded, reaches `pair -`
+// on standard input and never an argument, exit 3 is success, and the
+// install with no flag still ends the way it did.
+func TestInstallPs1PairShape(t *testing.T) {
+	raw, err := os.ReadFile(filepath.Join("..", "deploy", "install.ps1"))
+	if err != nil {
+		t.Fatal(err)
+	}
+	s := string(raw)
+	for _, want := range []string{
+		"param([switch]$Networked, [string]$Pair)",
+		"$Pair | & $exe pair -",
+		"elseif ($rc -eq 3)",
+		"Start-ScheduledTask -TaskName 'PrivataeBastion'",
+		"Restart-Service -Name 'PrivataeBastion'",
+		`Write-Host "Open a NEW terminal, then:  privatae-bastion pair <token>"`,
+	} {
+		if !strings.Contains(s, want) {
+			t.Errorf("install.ps1 lacks %q", want)
+		}
+	}
+	for _, bad := range []string{"pair $Pair", "pair -- $Pair", "-ArgumentList $Pair", "Write-Host $Pair", "$Pair\"", "'$Pair'"} {
+		if strings.Contains(s, bad) {
+			t.Errorf("install.ps1 must never put the code in an argument or the output: %q", bad)
+		}
+	}
+	check, fetch := strings.Index(s, "StartsWith('skp_')"), strings.Index(s, `Write-Host "Fetching manifest..."`)
+	if check < 0 || fetch < 0 || check > fetch {
+		t.Error("the pairing code must be checked before the manifest is fetched")
+	}
+}
+
+// The -Pair block itself, run by pwsh against a stand-in bastion
+// (testdata/install_ps1_pair.ps1). Skipped where pwsh is not installed.
+func TestInstallPs1PairBlockRunsUnderPwsh(t *testing.T) {
+	pwsh, err := exec.LookPath("pwsh")
+	if err != nil {
+		t.Skip("pwsh is not installed: install.ps1's -Pair block is checked only by TestInstallPs1PairShape here")
+	}
+	out, err := exec.Command(pwsh, "-NoProfile", "-NonInteractive", "-File",
+		filepath.Join("testdata", "install_ps1_pair.ps1"), filepath.Join("..", "deploy", "install.ps1")).CombinedOutput()
+	if err != nil || !strings.HasPrefix(strings.TrimSpace(string(out)), "ok:") {
+		t.Fatalf("%v\n%s", err, out)
+	}
+}

client-go/install_sh_test.go

@@ -3,10 +3,13 @@
 package main
 
 import (
+	"crypto/sha256"
+	"encoding/hex"
 	"os"
 	"os/exec"
 	"path/filepath"
 	"regexp"
+	"strings"
 	"testing"
 )
 
@@ -74,3 +77,358 @@ func TestInstallShKeepsAPairedLocalMachineLocal(t *testing.T) {
 		t.Fatal("a machine with no pairing gets the networked default")
 	}
 }
+
+// installShPrivatePIDs is what a test that reaches install.sh's
+// start_bastion runs under. start_bastion stops every copy of this user's
+// bastion it can see in /proc, and on a machine that runs a real bastion as
+// this user (root on a server) that would be the real one. So the test must
+// see only its own processes: nil when it already runs in a PID namespace of
+// its own (CI's container), the unshare prefix that makes one when it can,
+// and a skip otherwise.
+//
+// The machine's own PID namespace is the kernel's initial one, whose number
+// is fixed (PROC_PID_INIT_INO, 0xEFFFFFFC); any other is a namespace of its
+// own. NSpid in /proc/self/status cannot tell: inside a container /proc is
+// the container's, so it shows one level there too.
+func installShPrivatePIDs(t *testing.T) []string {
+	t.Helper()
+	ns, err := os.Readlink("/proc/self/ns/pid")
+	if err == nil && ns != "pid:[4026531836]" {
+		return nil
+	}
+	if err == nil && os.Geteuid() == 0 {
+		if u, err := exec.LookPath("unshare"); err == nil {
+			wrap := []string{u, "--pid", "--fork", "--mount-proc"}
+			if exec.Command(wrap[0], append(wrap[1:], "true")...).Run() == nil {
+				return wrap
+			}
+		}
+	}
+	t.Skip("install.sh's start_bastion stops every copy of this user's bastion; run this test in a PID namespace of its own (unshare --pid --fork --mount-proc, as root)")
+	return nil
+}
+
+// pairShSetup is a stand-in machine for install.sh: a log directory, a
+// home, and a PATH directory of stand-ins for systemctl, loginctl and sleep,
+// each logging what it was given. unit is how the stand-in systemd reports
+// the user unit: "steady" (one process, running) or "flapping" (a new
+// process on every look, auto-restarting).
+type pairShSetup struct {
+	dir, logs, bin, path, home string
+}
+
+func newPairShSetup(t *testing.T) *pairShSetup {
+	t.Helper()
+	d := t.TempDir()
+	s := &pairShSetup{dir: d, logs: filepath.Join(d, "log"), bin: filepath.Join(d, "bin"), path: filepath.Join(d, "path"), home: filepath.Join(d, "home")}
+	for _, p := range []string{s.logs, s.bin, s.path, s.home} {
+		if err := os.MkdirAll(p, 0o700); err != nil {
+			t.Fatal(err)
+		}
+	}
+	s.write(t, filepath.Join(s.path, "systemctl"), `#!/bin/sh
+echo "$*" >> "$LOGS/systemctl"
+case "$*" in
+  *"show -p MainPID --value"*)
+    if [ "$UNIT" = flapping ]; then n=$(cat "$LOGS/n" 2>/dev/null || echo 100); n=$((n + 1)); echo "$n" > "$LOGS/n"; echo "$n"; else echo 4242; fi ;;
+  *"show -p ActiveState --value"*) if [ "$UNIT" = flapping ]; then echo activating; else echo active; fi ;;
+  *"show -p SubState --value"*) if [ "$UNIT" = flapping ]; then echo auto-restart; else echo running; fi ;;
+esac
+exit 0
+`)
+	s.write(t, filepath.Join(s.path, "loginctl"), "#!/bin/sh\necho \"$*\" >> \"$LOGS/loginctl\"\nexit \"$LINGER_RC\"\n")
+	s.write(t, filepath.Join(s.path, "sleep"), "#!/bin/sh\nexit 0\n")
+	return s
+}
+
+func (s *pairShSetup) write(t *testing.T, p, body string) {
+	t.Helper()
+	if err := os.WriteFile(p, []byte(body), 0o700); err != nil {
+		t.Fatal(err)
+	}
+}
+
+func (s *pairShSetup) env(extra ...string) []string {
+	return append([]string{"PATH=" + s.path + ":/usr/bin:/bin", "HOME=" + s.home, "XDG_CONFIG_HOME=" + filepath.Join(s.home, ".config"),
+		"LOGS=" + s.logs, "TMPDIR=" + s.dir}, extra...)
+}
+
+// standInCopy puts a copy of this test binary at dir/privatae-bastion: run
+// with installShStandInRun it is a bastion that waits to be stopped, under
+// the program name install.sh looks for.
+func standInCopy(t *testing.T, dir string) string {
+	t.Helper()
+	self, err := os.Executable()
+	if err != nil {
+		t.Fatal(err)
+	}
+	b, err := os.ReadFile(self)
+	if err != nil {
+		t.Fatal(err)
+	}
+	p := filepath.Join(dir, "privatae-bastion")
+	if err := os.WriteFile(p, b, 0o755); err != nil {
+		t.Fatal(err)
+	}
+	return p
+}
+
+// pairShHarness runs install.sh's pairing functions against a stand-in
+// bastion, systemctl and loginctl. It returns the run's output, the log
+// directory and its error. With copyRunning, a copy of the bastion from another
+// path is running when the functions start, and log/copy says whether it
+// still was when they ended.
+func pairShHarness(t *testing.T, root, pairRC, lingerRC string) (string, string, error) {
+	t.Helper()
+	return pairShHarnessWith(t, root, pairRC, lingerRC, "steady", false)
+}
+
+func pairShHarnessWith(t *testing.T, root, pairRC, lingerRC, unit string, copyRunning bool) (string, string, error) {
+	t.Helper()
+	wrap := installShPrivatePIDs(t)
+	s := newPairShSetup(t)
+	fake := filepath.Join(s.bin, "privatae-bastion")
+	s.write(t, fake, `#!/bin/sh
+echo "HOME=$HOME $*" >> "$LOGS/argv"
+case "$1" in
+  pair) cat > "$LOGS/stdin"; exit "$PAIR_RC" ;;
+  status) echo "status: paired" ;;
+esac
+exit 0
+`)
+	copyPath := ""
+	if copyRunning {
+		other := filepath.Join(s.dir, "other-install")
+		if err := os.MkdirAll(other, 0o700); err != nil {
+			t.Fatal(err)
+		}
+		copyPath = standInCopy(t, other)
+	}
+	fns := installShFunc(t, "pair_as") + installShFunc(t, "bastion_copy") + installShFunc(t, "stop_user_copies") +
+		installShFunc(t, "user_unit_stays_up") + installShFunc(t, "start_bastion") + installShFunc(t, "pair_and_start")
+	script := fns + `
+if [ -n "$COPY" ]; then
+  "$COPY" ` + installShStandInRun + ` >/dev/null 2>&1 &
+  copy=$!
+  i=0
+  while ! bastion_copy "$copy" && [ "$i" -lt 100 ]; do i=$((i + 1)); /bin/sleep 0.05; done
+  bastion_copy "$copy" || { echo "the stand-in copy never started" >&2; exit 97; }
+fi
+rc=0
+pair_and_start "$1" "$2" "$3" linux || rc=$?
+if [ -n "$COPY" ]; then
+  if bastion_copy "$copy"; then echo alive > "$LOGS/copy"; kill -9 "$copy"; else echo gone > "$LOGS/copy"; fi
+fi
+exit "$rc"
+`
+	args := append(append([]string{}, wrap...), "sh", "-c", script, "sh", fake, "skp_INVENTEDCODE", root)
+	cmd := exec.Command(args[0], args[1:]...)
+	cmd.Env = s.env("PAIR_RC="+pairRC, "LINGER_RC="+lingerRC, "UNIT="+unit, "COPY="+copyPath)
+	out, err := cmd.CombinedOutput()
+	return string(out), s.logs, err
+}
+
+func readPairShLog(t *testing.T, dir, name string) string {
+	t.Helper()
+	b, _ := os.ReadFile(filepath.Join(dir, name))
+	return string(b)
+}
+
+// The pairing functions hand the code to `pair -` on standard input, never
+// as an argument, then write and start a systemd user unit, ask for
+// lingering, and end with one plain sentence. Exit 3 (already paired with
+// this Host) is success.
+func TestInstallShPairsOverStdinAndStartsAUserUnit(t *testing.T) {
+	out, logs, err := pairShHarness(t, "0", "0", "0")
+	if err != nil {
+		t.Fatalf("%v\n%s", err, out)
+	}
+	argv := readPairShLog(t, logs, "argv")
+	if !strings.Contains(argv, " pair -\n") || strings.Contains(argv, "skp_") {
+		t.Fatalf("the code must reach `pair -` on stdin and never an argument: %q", argv)
+	}
+	if got := readPairShLog(t, logs, "stdin"); got != "skp_INVENTEDCODE\n" {
+		t.Fatalf("pair's standard input: %q", got)
+	}
+	home := strings.TrimPrefix(strings.Fields(argv)[0], "HOME=")
+	unit, err := os.ReadFile(filepath.Join(home, ".config", "systemd", "user", "privatae-bastion.service"))
+	if err != nil || !regexp.MustCompile(`(?m)^ExecStart=\S+/privatae-bastion run$`).Match(unit) || !strings.Contains(string(unit), "WantedBy=default.target") {
+		t.Fatalf("the user unit: %v\n%s", err, unit)
+	}
+	sc := readPairShLog(t, logs, "systemctl")
+	for _, want := range []string{"--user daemon-reload", "--user enable privatae-bastion", "--user restart privatae-bastion"} {
+		if !strings.Contains(sc, want+"\n") {
+			t.Fatalf("systemctl was not asked to %q: %q", want, sc)
+		}
+	}
+	if !strings.Contains(readPairShLog(t, logs, "loginctl"), "enable-linger ") {
+		t.Fatal("lingering was not asked for")
+	}
+	if !strings.Contains(out, "status: paired") || !strings.HasSuffix(strings.TrimSpace(out),
+		"This machine is paired. The bastion runs as your systemd user service privatae-bastion, and starts at boot.") {
+		t.Fatalf("the ending: %s", out)
+	}
+
+	out, _, err = pairShHarness(t, "0", "3", "1")
+	if err != nil || !strings.Contains(out, "already paired with this Host") || !strings.Contains(out, "sudo loginctl enable-linger") {
+		t.Fatalf("exit 3 is success, and a refused linger says how to get it: %v\n%s", err, out)
+	}
+
+	out, logs, err = pairShHarness(t, "0", "1", "0")
+	if err == nil || strings.Contains(readPairShLog(t, logs, "systemctl"), "restart") || !strings.Contains(out, "pairing did not finish") {
+		t.Fatalf("a failed pair must stop before starting anything: %v\n%s", err, out)
+	}
+
+	out, logs, err = pairShHarness(t, "1", "0", "0")
+	if err != nil || !strings.Contains(readPairShLog(t, logs, "argv"), "HOME=/root ") ||
+		readPairShLog(t, logs, "systemctl") != "restart privatae-bastion\n" || strings.Contains(out, "user service") {
+		t.Fatalf("as root it pairs as the service's state and restarts the system service: %v\n%s\n%s", err, out, readPairShLog(t, logs, "systemctl"))
+	}
+}
+
+// Linux, as yourself: a copy of the bastion already running outside the
+// user unit (from a terminal, or another path) is stopped before the unit
+// starts, so the unit's copy is the one that serves; and a unit that does not
+// stay up is said plainly, with a failure, never reported as running.
+func TestInstallShStopsAnOutsideCopyAndChecksTheUnitStaysUp(t *testing.T) {
+	out, logs, err := pairShHarnessWith(t, "0", "0", "0", "steady", true)
+	if err != nil {
+		t.Fatalf("%v\n%s", err, out)
+	}
+	if got := strings.TrimSpace(readPairShLog(t, logs, "copy")); got != "gone" {
+		t.Fatalf("the copy running outside the unit must be stopped, it is %q\n%s", got, out)
+	}
+	if !strings.Contains(out, "Stopped 1 copy(ies) of the bastion running outside its service") {
+		t.Fatalf("the stop is said: %s", out)
+	}
+	sc := readPairShLog(t, logs, "systemctl")
+	if i, j := strings.Index(sc, "--user stop privatae-bastion\n"), strings.Index(sc, "--user restart privatae-bastion\n"); i < 0 || j < i {
+		t.Fatalf("the unit is stopped before the copies and started after: %q", sc)
+	}
+	if !strings.HasSuffix(strings.TrimSpace(out), "This machine is paired. The bastion runs as your systemd user service privatae-bastion, and starts at boot.") {
+		t.Fatalf("the ending: %s", out)
+	}
+
+	out, _, err = pairShHarnessWith(t, "0", "0", "0", "flapping", false)
+	if err == nil || !strings.Contains(out, "is not staying up") || !strings.Contains(out, "activating/auto-restart") ||
+		!strings.Contains(out, "journalctl --user -u privatae-bastion") || strings.Contains(out, "The bastion runs as your systemd user service") {
+		t.Fatalf("a unit that restarts must be reported as not running, and fail: %v\n%s", err, out)
+	}
+}
+
+// The whole of install.sh, the card's way: the code in PRIVATAE_PAIR_CODE
+// and no argument. Every program it starts (stand-ins for uname, id, curl,
+// printf, systemctl, loginctl and sleep, and the downloaded bastion) records
+// its own arguments, the command line of the shell that started it, and
+// whether the code is in its environment. The code must reach `pair -` on
+// standard input and appear in none of those. Nothing leaves this machine:
+// curl is a stand-in serving a manifest and a stand-in bastion.
+func TestInstallShTakesTheCodeOnlyFromTheEnvironment(t *testing.T) {
+	wrap := installShPrivatePIDs(t)
+	s := newPairShSetup(t)
+	const code = "skp_eyJ2IjoxLCJ0IjoiSU5WRU5URUQtRU5WLUNPREUifQ"
+	record := `echo "$(basename "$0") argv=[$*] parent=[$(tr '\0' ' ' < /proc/$PPID/cmdline)] env=[${PRIVATAE_PAIR_CODE+set}] envcode=[$(env | grep -c "` + code + `")]" >> "$LOGS/procs"
+`
+	bastion := "#!/bin/sh\n" + record + `case "$1" in
+  pair) cat > "$LOGS/stdin" ;;
+  status) echo "status: paired" ;;
+esac
+exit 0
+`
+	s.write(t, filepath.Join(s.dir, "bastion.bin"), bastion)
+	sum := sha256.Sum256([]byte(bastion))
+	s.write(t, filepath.Join(s.dir, "version.json"), "{\n  \"linux-amd64\": {\n    \"url\": \"https://dl.privatae.ai/dl/privatae-bastion-linux-amd64?v=0.0.0\",\n    \"sha256\": \""+hex.EncodeToString(sum[:])+"\"\n  }\n}\n")
+	stand := map[string]string{
+		"uname":  `case "$1" in -s) echo Linux ;; -m) echo x86_64 ;; *) echo Linux ;; esac`,
+		"id":     `case "$1" in -u) echo 1000 ;; -un) echo tester ;; *) echo "uid=1000(tester)" ;; esac`,
+		"curl":   `for a; do o=$a; done; case "$2" in */version.json) cp "$STAND/version.json" "$o" ;; *) cp "$STAND/bastion.bin" "$o" ;; esac`,
+		"printf": `exec /usr/bin/printf "$@"`,
+	}
+	for name, body := range stand {
+		s.write(t, filepath.Join(s.path, name), "#!/bin/sh\n"+record+body+"\n")
+	}
+	for _, name := range []string{"systemctl", "loginctl", "sleep"} {
+		p := filepath.Join(s.path, name)
+		b, _ := os.ReadFile(p)
+		s.write(t, p, strings.Replace(string(b), "#!/bin/sh\n", "#!/bin/sh\n"+record, 1))
+	}
+	sh, err := filepath.Abs(filepath.Join("..", "deploy", "install.sh"))
+	if err != nil {
+		t.Fatal(err)
+	}
+	args := append(append([]string{}, wrap...), "sh", sh)
+	cmd := exec.Command(args[0], args[1:]...)
+	cmd.Env = s.env("PRIVATAE_PAIR_CODE="+code, "STAND="+s.dir, "LINGER_RC=0", "UNIT=steady")
+	out, err := cmd.CombinedOutput()
+	if err != nil {
+		t.Fatalf("%v\n%s", err, out)
+	}
+	if got := readPairShLog(t, s.logs, "stdin"); got != code+"\n" {
+		t.Fatalf("pair's standard input: %q\n%s", got, out)
+	}
+	procs := readPairShLog(t, s.logs, "procs")
+	for _, who := range []string{"uname argv=[-s]", "curl argv=[", "privatae-bastion argv=[pair -]", "privatae-bastion argv=[status]", "systemctl argv=[--user restart privatae-bastion]"} {
+		if !strings.Contains(procs, who) {
+			t.Fatalf("no record of %q: the stand-ins did not run as expected\n%s\n%s", who, procs, out)
+		}
+	}
+	if strings.Contains(procs, code) || strings.Contains(procs, "INVENTED-ENV-CODE") {
+		t.Fatalf("the code is in a program's arguments or its shell's command line:\n%s", procs)
+	}
+	if strings.Contains(procs, "env=[set]") || !strings.Contains(procs, "envcode=[0]") || strings.Contains(procs, "envcode=[1]") {
+		t.Fatalf("a program the installer started inherited the code in its environment:\n%s", procs)
+	}
+	if strings.Contains(string(out), code) {
+		t.Fatalf("the installer printed the code:\n%s", out)
+	}
+	if !strings.HasSuffix(strings.TrimSpace(string(out)), "https://privatae.ai/bastion/LICENSE.txt") || !strings.Contains(string(out), "This machine is paired.") {
+		t.Fatalf("the ending: %s", out)
+	}
+}
+
+// A PRIVATAE_PAIR_CODE that is empty or not a whole pairing code is refused
+// before anything is downloaded, and never echoed; so is any argument, a
+// code given as one (the removed --pair, or the code alone) included.
+//
+// The script runs with stand-ins for id (not root) and curl (records that it
+// was reached, fetches nothing), so an installer whose refusal broke can
+// neither reach the network nor install anything as root on the machine
+// running the test: it fails here instead.
+func TestInstallShRefusesABadPairCodeBeforeDownloading(t *testing.T) {
+	const code = "skp_eyJ2IjoxfQ"
+	stand := t.TempDir()
+	for name, body := range map[string]string{
+		"id":   `case "$1" in -u) echo 1000 ;; -un) echo tester ;; *) echo "uid=1000(tester)" ;; esac`,
+		"curl": `echo "REACHED-THE-DOWNLOAD" >&2; exit 1`,
+	} {
+		if err := os.WriteFile(filepath.Join(stand, name), []byte("#!/bin/sh\n"+body+"\n"), 0o700); err != nil {
+			t.Fatal(err)
+		}
+	}
+	for _, c := range []struct {
+		env  []string
+		args []string
+	}{
+		{[]string{"PRIVATAE_PAIR_CODE="}, nil},
+		{[]string{"PRIVATAE_PAIR_CODE=skp_"}, nil},
+		{[]string{"PRIVATAE_PAIR_CODE=skb_aG9tZS5zZWNyZXQteA"}, nil},
+		{[]string{"PRIVATAE_PAIR_CODE=" + code + " trailing"}, nil},
+		{[]string{"PRIVATAE_PAIR_CODE=" + code + "%3D"}, nil},
+		{nil, []string{"--pair", code}},
+		{nil, []string{"--pair=" + code}},
+		{nil, []string{code}},
+		{nil, []string{"--networkd"}},
+	} {
+		home := t.TempDir()
+		cmd := exec.Command("sh", append([]string{filepath.Join("..", "deploy", "install.sh")}, c.args...)...)
+		cmd.Env = append([]string{"PATH=" + stand + ":/usr/bin:/bin", "HOME=" + home, "TMPDIR=" + home}, c.env...)
+		out, err := cmd.CombinedOutput()
+		ee, ok := err.(*exec.ExitError)
+		if !ok || ee.ExitCode() != 2 || strings.Contains(string(out), "Fetching manifest") || strings.Contains(string(out), "REACHED-THE-DOWNLOAD") {
+			t.Fatalf("%v %v: want exit 2 before the download, got %v\n%s", c.env, c.args, err, out)
+		}
+		if strings.Contains(string(out), code) || strings.Contains(string(out), "skb_") || strings.Contains(string(out), "networkd") {
+			t.Fatalf("%v %v: the refusal echoes what it was given: %s", c.env, c.args, out)
+		}
+	}
+}

client-go/main.go

@@ -37,6 +37,13 @@ Usage:
                                that CA alone (name host.cseries.internal), the lanes go to
                                the lane port the Host names, and the CA is pinned for life.
                                No coder runs over this pairing
+  privatae-bastion pair <pairing code skp_…>
+                               the same pairing from the one code a Cloud Host's card gives:
+                               it carries the enroll address and the CA's fingerprint, and
+                               the CA is taken from the enroll port only under that
+                               fingerprint. On a local machine that already serves a Host,
+                               it asks here whether to add this one as well. Exit 3: already
+                               paired with this Host, nothing changed
   privatae-bastion run            bring up the tunnel + lanes for EVERY paired host
                                (a loopback control port per host for the verbs below:
                                127.0.0.1:7878, then 7879, …)
@@ -188,7 +195,9 @@ func takeHostFlag(args []string) (string, []string) {
 }
 
 const pairUsage = "usage: privatae-bastion pair [--replace] [--redeem-url unix:///<socket> | --redeem-url https://<host>:<port>/<path> --host-ca <pem file>] <token> | -\n" +
-	"  - reads the token from standard input, so it stays out of the process list and shell history"
+	"       privatae-bastion pair <pairing code skp_…> | -\n" +
+	"  - reads the token or pairing code from standard input, so it stays out of the process list and shell history\n" +
+	"  exit status: 0 paired, 3 already paired with this Host (nothing changed), anything else a failure"
 
 // parsePairArgs reads `pair`'s flags in any order: --replace, --redeem-url
 // for a Host with no platform (pair_unix.go, pair_tcp.go) and --host-ca for
@@ -258,6 +267,15 @@ func main() {
 			os.Exit(2)
 		}
 		err = cmdPair(token, redeemURL, hostCA, replace)
+		// Already paired with this Host, nothing changed: its own exit status,
+		// so the installers (install.ps1 -Pair, install.sh with
+		// PRIVATAE_PAIR_CODE) report "already connected".
+		var already *alreadyPairedError
+		if errors.As(err, &already) {
+			auditFlush(auditFlushOnExit)
+			fmt.Fprintln(os.Stderr, already)
+			os.Exit(pairExitAlreadyPaired)
+		}
 	case "run":
 		err = cmdRun()
 	case "observe:baseline":

client-go/main_test.go

@@ -36,8 +36,13 @@ import (
 	"os"
 	"strings"
 	"testing"
+	"time"
 )
 
+// installShStandInRun is the argument that makes this test binary stand in
+// for a running bastion (TestMain).
+const installShStandInRun = "install-sh-stand-in-run"
+
 func TestMain(m *testing.M) {
 	// The op sandbox re-execs its own binary (ops_exec_linux.go); under
 	// `go test` that binary is this one, so the child must be answered here
@@ -62,6 +67,13 @@ func TestMain(m *testing.M) {
 	if len(os.Args) >= 3 && os.Args[1] == rootExecConnectSubcommand {
 		os.Exit(rootExecConnectMain(os.Args[2:]))
 	}
+	// install_sh_test.go runs a copy of this binary named privatae-bastion as
+	// a bastion left running outside its service: it only waits to be
+	// stopped, and never starts the suite.
+	if len(os.Args) >= 2 && os.Args[1] == installShStandInRun {
+		time.Sleep(2 * time.Minute)
+		os.Exit(0)
+	}
 	// Likewise when git runs this binary as the bastion's credential helper
 	// (claims_git_test.go): answer as the helper, with the config dir the
 	// test named, and never start the suite.

client-go/mode.go

@@ -88,11 +88,13 @@ func setBoxMode(mode string) error {
 		}
 	}
 	if mode == modeLocal {
-		// Going back to local must not strand hosts: a local box serves ONE host,
-		// so with several pairings the box would be lying about its own rule.
+		// Going back to local must not strand hosts: a local box serves a second
+		// host only on a yes typed at this machine (pair_terminal.go), and these
+		// were paired under the networked rules, so with several pairings the box
+		// would serve hosts nobody here said yes to.
 		cfgs, err := loadPairings()
 		if err == nil && len(cfgs) > 1 {
-			return fmt.Errorf("cannot switch to local mode: %d hosts are paired and a local bastion serves one — remove the others first", len(cfgs))
+			return fmt.Errorf("cannot switch to local mode: %d hosts are paired, and a local bastion adds a second host only on a yes typed at this machine — remove the others first, then pair them again here", len(cfgs))
 		}
 		if currentAnchor() != nil {
 			return errors.New("cannot switch to local mode: this box is anchored (anchor.json) — anchoring is a networked-mode concept")

client-go/pair.go

@@ -163,10 +163,12 @@ type redeemResp struct {
 // mode rule, and the anchoring rule. Returns the existing pairing on a
 // --replace and the state the new pairing file must carry.
 //
-//   - LOCAL mode (mode.go): one host, full stop. A second `pair` is refused with
-//     a plain message; only --replace of the one host is allowed. This is the
-//     entire protection for a single-user machine — a second host appearing
-//     means someone else got a token onto the box.
+//   - LOCAL mode (mode.go): one host unless the person says otherwise. A
+//     second `pair` is refused here with localSecondHostError; `pair` itself
+//     turns that into a question asked on this machine's terminal
+//     (pair_terminal.go), and every other caller keeps the refusal. On a
+//     single-user machine a second host appearing unasked means someone else
+//     got a token onto the box, so only a yes typed here adds one.
 //   - NETWORKED + anchored (anchor.go): every pairing after the anchor is written
 //     PENDING. It gets nothing until the anchor host's grant arrives.
 //   - --replace keeps the pairing's current state: rotating credentials is not
@@ -191,11 +193,14 @@ func pairPrecheck(cfgs []*Config, handle string, replace, forceActive bool) (exi
 		return existing, existing.State, nil
 	}
 	if boxMode() == modeLocal && len(cfgs) > 0 {
-		return nil, "", fmt.Errorf("this bastion is in local mode and already serves %s — a local bastion serves one host. "+
-			"To rotate that host's credentials: `privatae-bastion pair --replace <token>`. "+
-			"To serve several hosts, reinstall as a networked bastion (install.sh --networked, root) and anchor it",
-			cfgs[0].HostName)
+		return nil, "", &localSecondHostError{serving: cfgs[0].HostName}
 	}
+	return pairPrecheckState(forceActive)
+}
+
+// pairPrecheckState is the state a new pairing gets once pairPrecheck's walls
+// are passed: active for claim-anchor, pending behind an anchor, else "".
+func pairPrecheckState(forceActive bool) (*Config, string, error) {
 	if forceActive {
 		return nil, pairingActive, nil
 	}
@@ -205,8 +210,73 @@ func pairPrecheck(cfgs []*Config, handle string, replace, forceActive bool) (exi
 	return nil, "", nil
 }
 
+// localSecondHostError is pairPrecheck's refusal on a local machine that
+// already serves a host. cmdPair asks the person instead (confirmAddHost).
+type localSecondHostError struct{ serving string }
+
+func (e *localSecondHostError) Error() string { return localOneHostRefusal(e.serving) }
+
+// localOneHostRefusal says why a second host was not added to a local
+// bastion and what the person can do, in this system's own words. A networked
+// reinstall starts a bastion with its own state, so it says plainly that the
+// host already here would have to be paired again.
+func localOneHostRefusal(serving string) string {
+	networked := "reinstall it as root with install.sh --networked"
+	if runtime.GOOS == "windows" {
+		networked = "reinstall it from an Administrator PowerShell with install.ps1 -Networked"
+	}
+	return fmt.Sprintf("this bastion is in local mode and already serves %s, and it adds another Host only when you "+
+		"answer yes at this computer's terminal. To rotate %s's credentials instead: `privatae-bastion pair --replace <token>`. "+
+		"A machine that other people's Hosts pair to is a networked bastion: %s. That makes a new bastion with "+
+		"state of its own, so %s has to be paired with it again.", serving, serving, networked, serving)
+}
+
+// alreadyPairedError: the host a pair names is already paired here, and
+// nothing was changed. `pair` exits pairExitAlreadyPaired on it, so an
+// installer can tell "already connected" from a failure.
+type alreadyPairedError struct{ host, msg string }
+
+func (e *alreadyPairedError) Error() string { return e.msg }
+
+// pairExitAlreadyPaired is `pair`'s exit status for alreadyPairedError.
+const pairExitAlreadyPaired = 3
+
+// sameNameOtherHost refuses, as a plain failure and never as
+// alreadyPairedError, a pair whose Host has the name of prev but trusts
+// another CA (wantCA, its fingerprint). A Cloud Host's name can repeat; its CA
+// cannot, so that is another Host and never "already connected". nil when
+// prev is nil or holds that same CA.
+func sameNameOtherHost(prev *Config, wantCA string) error {
+	if prev == nil || caSHA256(prev.CACert) == wantCA {
+		return nil
+	}
+	return fmt.Errorf("this computer already serves a different Host named %s (its certificate is not this one's), "+
+		"and one bastion cannot serve two Hosts of the same name yet; nothing was paired", prev.HostName)
+}
+
+func alreadyPairedRefusal(host string) error {
+	return &alreadyPairedError{host: host, msg: fmt.Sprintf("already paired with %s — run `privatae-bastion pair --replace <token>` to rotate its credentials", host)}
+}
+
+// pairOpts are what `pair` brings beyond the token: where to redeem, the
+// Host CA as a file or as a pairing code's fingerprint, and the person to ask
+// before a local machine adds a second host (nil: refuse, as every caller but
+// `pair` does).
+type pairOpts struct {
+	redeemURL   string
+	hostCAFile  string
+	caSHA256    string
+	replace     bool
+	forceActive bool
+	askSecond   func(serving, newHost string) (bool, error)
+}
+
 func cmdPair(token, redeemURL, hostCAFile string, replace bool) error {
-	cfg, all, err := pairWithTokenVia(token, redeemURL, hostCAFile, replace, false)
+	token, opts, err := pairOptsFor(token, redeemURL, hostCAFile, replace)
+	if err != nil {
+		return err
+	}
+	cfg, all, err := pairWith(token, opts)
 	if err != nil {
 		return err
 	}
@@ -236,6 +306,26 @@ func cmdPair(token, redeemURL, hostCAFile string, replace bool) error {
 	return nil
 }
 
+// pairOptsFor is what `pair`'s arguments come to: the token to redeem and
+// the options for it, the person at this machine to ask about a second host
+// among them. A pairing code (pair_code.go) carries the redeem address and the
+// Host CA's fingerprint itself, so it takes neither flag.
+func pairOptsFor(token, redeemURL, hostCAFile string, replace bool) (string, pairOpts, error) {
+	opts := pairOpts{redeemURL: redeemURL, hostCAFile: hostCAFile, replace: replace, askSecond: confirmAddHost}
+	if !isPairCode(token) {
+		return token, opts, nil
+	}
+	if redeemURL != "" || hostCAFile != "" {
+		return "", opts, errors.New("a pairing code (skp_…) carries its own address and certificate; give it alone, without --redeem-url or --host-ca")
+	}
+	pc, err := decodePairCode(token)
+	if err != nil {
+		return "", opts, err
+	}
+	opts.redeemURL, opts.caSHA256 = pc.RedeemURL, pc.CASHA256
+	return pc.Token, opts, nil
+}
+
 // pairReport is what `pair` prints once the pairing stands. Whatever the form
 // (anchored just now, over TCP, over a unix socket, pending, or over the
 // tunnel), it ends by saying to enrol a second factor when this pairing has
@@ -338,6 +428,14 @@ func pairWithTokenAt(token, redeemURL string, replace, forceActive bool) (*Confi
 // redeem URL needs (pair_tcp.go): the Host's enroll port, trusted through
 // that CA alone. A unix:// or platform redeem takes no --host-ca.
 func pairWithTokenVia(token, redeemURL, hostCAFile string, replace, forceActive bool) (*Config, []*Config, error) {
+	return pairWith(token, pairOpts{redeemURL: redeemURL, hostCAFile: hostCAFile, replace: replace, forceActive: forceActive})
+}
+
+// pairWith is every pairing's one path. opts.caSHA256 set (a pairing code)
+// takes the Host CA from the enroll port once the walls below are passed,
+// kept only under that fingerprint (fetchPinnedHostCA).
+func pairWith(token string, opts pairOpts) (*Config, []*Config, error) {
+	redeemURL, hostCAFile, replace, forceActive := opts.redeemURL, opts.hostCAFile, opts.replace, opts.forceActive
 	// ONE BASTION PER MACHINE, and this is the check that matters most.
 	//
 	// It is FIRST on purpose. loadPairings below reaches pairingsDir -> MkdirAll,
@@ -367,11 +465,16 @@ func pairWithTokenVia(token, redeemURL, hostCAFile string, replace, forceActive
 		if err != nil {
 			return nil, nil, err
 		}
-		if hostCAFile == "" {
+		switch {
+		case opts.caSHA256 != "":
+			// A pairing code: the CA comes from the enroll port after the
+			// walls, under the code's fingerprint.
+		case hostCAFile == "":
 			return nil, nil, errors.New("--redeem-url https://… needs --host-ca <the Host's CA, PEM>: it is the only certificate the redeem trusts")
-		}
-		if hostCA, err = loadHostCA(hostCAFile); err != nil {
-			return nil, nil, err
+		default:
+			if hostCA, err = loadHostCA(hostCAFile); err != nil {
+				return nil, nil, err
+			}
 		}
 		tcpRedeem, transport = u, transportTCP
 	default:
@@ -397,12 +500,41 @@ func pairWithTokenVia(token, redeemURL, hostCAFile string, replace, forceActive
 		return nil, nil, err
 	}
 	existing, state, err := pairPrecheck(cfgs, handle, replace, forceActive)
+	var second *localSecondHostError
+	if errors.As(err, &second) && opts.askSecond != nil {
+		yes, aerr := opts.askSecond(second.serving, handle)
+		if aerr != nil {
+			return nil, nil, aerr
+		}
+		if !yes {
+			return nil, nil, fmt.Errorf("nothing was paired: %s stays the only Host this computer serves", second.serving)
+		}
+		existing, state, err = pairPrecheckState(forceActive)
+	}
+	// The CA this pair trusts, as a fingerprint: the pairing code's, or that
+	// of the --host-ca file. "" for a platform or unix-socket pairing, whose
+	// CA comes back in the answer.
+	wantCA := opts.caSHA256
+	if wantCA == "" && hostCA != "" {
+		wantCA = caSHA256(hostCA)
+	}
+	var already *alreadyPairedError
+	if errors.As(err, &already) && wantCA != "" {
+		if refusal := sameNameOtherHost(pairingFor(cfgs, handle), wantCA); refusal != nil {
+			return nil, nil, refusal
+		}
+	}
 	if err != nil {
 		return nil, nil, err
 	}
 	if err := replaceKeepsTransport(existing, transport); err != nil {
 		return nil, nil, err
 	}
+	if tcpRedeem != nil && hostCA == "" {
+		if hostCA, err = fetchPinnedHostCA(tcpRedeem, opts.caSHA256); err != nil {
+			return nil, nil, err
+		}
+	}
 	if tcpRedeem != nil {
 		if err := tcpPinRefusal(existing, hostCA); err != nil {
 			return nil, nil, err
@@ -438,7 +570,7 @@ func pairWithTokenVia(token, redeemURL, hostCAFile string, replace, forceActive
 		if prev := pairingFor(cfgs, rr.hostName()); prev != nil && validHostName(rr.hostName()) {
 			existing = prev
 			if !replace {
-				return nil, nil, fmt.Errorf("already paired with %s — run `privatae-bastion pair --replace <token>` to rotate its credentials", prev.HostName)
+				return nil, nil, alreadyPairedRefusal(prev.HostName)
 			}
 			if err := replaceKeepsTransport(existing, transportUnix); err != nil {
 				return nil, nil, err
@@ -463,7 +595,10 @@ func pairWithTokenVia(token, redeemURL, hostCAFile string, replace, forceActive
 		if prev := pairingFor(cfgs, rr.hostName()); prev != nil && validHostName(rr.hostName()) {
 			existing = prev
 			if !replace {
-				return nil, nil, fmt.Errorf("already paired with %s — run `privatae-bastion pair --replace <token>` to rotate its credentials", prev.HostName)
+				if refusal := sameNameOtherHost(prev, caSHA256(hostCA)); refusal != nil {
+					return nil, nil, refusal
+				}
+				return nil, nil, alreadyPairedRefusal(prev.HostName)
 			}
 			if err := replaceKeepsTransport(existing, transportTCP); err != nil {
 				return nil, nil, err
@@ -531,7 +666,7 @@ func pairWithTokenVia(token, redeemURL, hostCAFile string, replace, forceActive
 	if prev := pairingFor(cfgs, rr.HostName); prev != nil {
 		existing = prev
 		if !replace {
-			return nil, nil, fmt.Errorf("already paired with %s — run `privatae-bastion pair --replace <token>` to rotate its credentials", prev.HostName)
+			return nil, nil, alreadyPairedRefusal(prev.HostName)
 		}
 	}
 	opSecret, err := genSecret(24)

client-go/pair_code.go

@@ -0,0 +1,254 @@
+package main
+
+// pair_code.go: the pairing code a Host's "Set up a bastion" card hands out,
+// so pairing a machine is one pasted line.
+//
+//	privatae-bastion pair skp_…        or        … | privatae-bastion pair -
+//
+// The code is the single-use token plus the two things the person used to copy
+// by hand: the Host's enroll address and its CA. The CA does not travel; its
+// fingerprint does. The bastion takes the CA from the enroll port's own TLS
+// chain and keeps it only when its SHA-256 is the one in the code, so the trust
+// is the same as `--host-ca`: the fingerprint comes from the owner's own
+// signed-in card, as the PEM did. From there the pairing is exactly
+// `pair --redeem-url <u> --host-ca <that CA> <t>`.
+//
+// No error here repeats the code, for the reason pair_stdin.go gives: a log of
+// a failed install must not hold the token.
+
+import (
+	"bytes"
+	"context"
+	"crypto/sha256"
+	"crypto/tls"
+	"crypto/x509"
+	"encoding/base64"
+	"encoding/hex"
+	"encoding/json"
+	"encoding/pem"
+	"errors"
+	"fmt"
+	"net"
+	"net/url"
+	"strings"
+	"time"
+)
+
+// pairCodePrefix marks a pairing code; a bare token is skb_….
+const pairCodePrefix = "skp_"
+
+// pairCodeVersion is the one layout this bastion reads.
+const pairCodeVersion = 1
+
+// pairCode is a decoded pairing code: where to redeem, the Host CA's
+// fingerprint, and the token.
+type pairCode struct {
+	RedeemURL string // "u": the Host's enroll port, https://<host>:<port>/<path>
+	CASHA256  string // "ca": SHA-256 of the Host CA certificate's DER, lowercase hex
+	Token     string // "t": the skb_ token
+}
+
+func isPairCode(s string) bool { return strings.HasPrefix(s, pairCodePrefix) }
+
+// decodePairCode reads skp_<base64url(JSON)>: exactly the keys v, u, ca and t,
+// v the one version this bastion knows, u an enroll URL parseTCPRedeemURL
+// takes, ca 64 lowercase hex digits and t a token decodeToken takes.
+func decodePairCode(code string) (pairCode, error) {
+	var pc pairCode
+	bad := func(why string) (pairCode, error) {
+		return pairCode{}, fmt.Errorf("the pairing code is not one this bastion can read (%s); copy the whole line from the card again", why)
+	}
+	raw, err := base64.RawURLEncoding.DecodeString(strings.TrimPrefix(code, pairCodePrefix))
+	if err != nil {
+		return bad("it is not base64url")
+	}
+	var fields map[string]json.RawMessage
+	if err := json.Unmarshal(raw, &fields); err != nil {
+		return bad("it holds no JSON object")
+	}
+	// A map keeps the last of two same-named keys, so "exactly these four"
+	// is counted on the object as written: a key given twice is an extra key.
+	if n, err := jsonObjectKeyCount(raw); err != nil || n != len(fields) {
+		return bad("it names a field twice")
+	}
+	if len(fields) != 4 {
+		return bad(fmt.Sprintf("it has %d fields, and a pairing code has 4", len(fields)))
+	}
+	var v int
+	if err := json.Unmarshal(fields["v"], &v); err != nil {
+		return bad("its version is missing")
+	}
+	if v != pairCodeVersion {
+		return pairCode{}, fmt.Errorf("the pairing code is version %d, and this bastion reads version %d: update the bastion and pair again", v, pairCodeVersion)
+	}
+	for k, dst := range map[string]*string{"u": &pc.RedeemURL, "ca": &pc.CASHA256, "t": &pc.Token} {
+		if err := json.Unmarshal(fields[k], dst); err != nil || *dst == "" {
+			return bad("its " + k + " field is missing")
+		}
+	}
+	if _, err := parseTCPRedeemURL(pc.RedeemURL); err != nil {
+		return bad("its address is not an https enroll address")
+	}
+	if len(pc.CASHA256) != 64 || strings.ToLower(pc.CASHA256) != pc.CASHA256 {
+		return bad("its certificate fingerprint is not 64 lowercase hex digits")
+	}
+	if _, err := hex.DecodeString(pc.CASHA256); err != nil {
+		return bad("its certificate fingerprint is not hex")
+	}
+	if !strings.HasPrefix(pc.Token, "skb_") {
+		return bad("it carries no pairing token")
+	}
+	if _, _, err := decodeToken(pc.Token); err != nil {
+		return bad("its pairing token is malformed")
+	}
+	return pc, nil
+}
+
+// jsonObjectKeyCount counts the keys of the JSON object raw as written,
+// repeats included. raw has already decoded as an object.
+func jsonObjectKeyCount(raw []byte) (int, error) {
+	dec := json.NewDecoder(bytes.NewReader(raw))
+	if _, err := dec.Token(); err != nil { // the opening brace
+		return 0, err
+	}
+	n := 0
+	for dec.More() {
+		if _, err := dec.Token(); err != nil { // the key
+			return 0, err
+		}
+		var v json.RawMessage
+		if err := dec.Decode(&v); err != nil {
+			return 0, err
+		}
+		n++
+	}
+	return n, nil
+}
+
+// pairAnswerTimeout is how long the enroll port has to answer the first
+// connection. A Cloud Host's pairing port drops every address but the one the
+// card opened it to, so a pair from anywhere else gets no answer at all, and
+// without this it would wait for the system's own connect timeout, minutes.
+// A variable so a test can shorten it; nothing else assigns it.
+var pairAnswerTimeout = 10 * time.Second
+
+// pairDial dials the enroll port. A variable so a test can stand in a port
+// that never answers; nothing else assigns it.
+var pairDial = (&net.Dialer{}).DialContext
+
+// pairWindowError is what a pair says when the Host's enroll port did not
+// answer: the plain reason, which is nearly always the pairing window. A type
+// of its own so the redeem's HTTP client, which wraps every dial error in the
+// request's URL, can hand it on as it is.
+type pairWindowError struct{ host string }
+
+func (e *pairWindowError) Error() string {
+	return fmt.Sprintf("%s's pairing port didn't answer within %s. A Cloud Host opens it only to the address "+
+		"your browser used when you opened \"Set up a bastion\", for 15 minutes. Pair from that network, or "+
+		"on the card choose \"Pairing a machine on another network?\" and give this machine's address. Nothing was paired.",
+		e.host, pairAnswerTimeout)
+}
+
+// dialEnrollPort opens a TCP connection to the redeem URL's host and port
+// within pairAnswerTimeout, or says why not in plain words.
+func dialEnrollPort(ctx context.Context, u *url.URL) (net.Conn, error) {
+	addr := u.Host
+	if u.Port() == "" {
+		addr = net.JoinHostPort(u.Hostname(), "443")
+	}
+	ctx, cancel := context.WithTimeout(ctx, pairAnswerTimeout)
+	defer cancel()
+	c, err := pairDial(ctx, "tcp", addr)
+	if err == nil {
+		return c, nil
+	}
+	var ne net.Error
+	if errors.Is(err, context.DeadlineExceeded) || (errors.As(err, &ne) && ne.Timeout()) {
+		return nil, &pairWindowError{host: u.Hostname()}
+	}
+	return nil, fmt.Errorf("could not reach %s's pairing port: %v; nothing was paired", u.Hostname(), err)
+}
+
+// fetchPinnedHostCA takes the Host CA from the enroll port's TLS chain and
+// returns it as PEM, only when it is a CA whose SHA-256 over its DER is
+// wantSHA and the port's own certificate verifies under it alone for
+// tcpServerName, the check hostCATLS makes on every later connection. No
+// system roots are consulted at any point.
+func fetchPinnedHostCA(u *url.URL, wantSHA string) (string, error) {
+	conn, err := dialEnrollPort(context.Background(), u)
+	if err != nil {
+		return "", err
+	}
+	defer conn.Close()
+	var caPEM string
+	tc := &tls.Config{
+		ServerName: tcpServerName, MinVersion: tls.VersionTLS12,
+		// The chain is checked by verifyPinnedChain below, against the pinned
+		// CA alone; the system roots must play no part, so the default
+		// verification is the thing turned off here.
+		InsecureSkipVerify: true,
+		VerifyConnection: func(cs tls.ConnectionState) error {
+			p, err := verifyPinnedChain(cs.PeerCertificates, wantSHA)
+			caPEM = p
+			return err
+		},
+	}
+	_ = conn.SetDeadline(time.Now().Add(30 * time.Second))
+	tlsConn := tls.Client(conn, tc)
+	if err := tlsConn.Handshake(); err != nil {
+		return "", fmt.Errorf("%s's pairing port: %v; nothing was paired", u.Hostname(), err)
+	}
+	_ = tlsConn.Close()
+	return caPEM, nil
+}
+
+// verifyPinnedChain picks the pinned CA out of a presented chain and checks
+// the leaf against it. The leaf is chain[0]; the CA is any later certificate
+// whose SHA-256 is wantSHA.
+func verifyPinnedChain(chain []*x509.Certificate, wantSHA string) (string, error) {
+	if len(chain) == 0 {
+		return "", errors.New("the Host's pairing port presented no certificate")
+	}
+	var ca *x509.Certificate
+	sawCA := false
+	for _, c := range chain[1:] {
+		if !c.IsCA {
+			continue
+		}
+		sawCA = true
+		sum := sha256.Sum256(c.Raw)
+		if hex.EncodeToString(sum[:]) == wantSHA {
+			ca = c
+			break
+		}
+	}
+	if ca == nil {
+		if sawCA {
+			return "", errors.New("the Host's pairing port presented a certificate authority other than the one this pairing code names — refusing")
+		}
+		return "", errors.New("the Host's pairing port did not present its certificate authority, so this pairing code cannot be checked — refusing (the Host needs a newer release, or pair with --host-ca)")
+	}
+	roots := x509.NewCertPool()
+	roots.AddCert(ca)
+	inter := x509.NewCertPool()
+	for _, c := range chain[1:] {
+		if c != ca {
+			inter.AddCert(c)
+		}
+	}
+	if _, err := chain[0].Verify(x509.VerifyOptions{Roots: roots, Intermediates: inter, DNSName: tcpServerName}); err != nil {
+		return "", fmt.Errorf("the Host's pairing port certificate is not signed by the certificate authority this pairing code names: %v — refusing", err)
+	}
+	return string(pem.EncodeToMemory(&pem.Block{Type: "CERTIFICATE", Bytes: ca.Raw})), nil
+}
+
+// caSHA256 is the fingerprint a pairing code carries for a PEM CA: SHA-256 of
+// the first certificate's DER, lowercase hex. "" when the PEM holds none.
+func caSHA256(caPEM string) string {
+	certs := pemCerts(caPEM)
+	if len(certs) == 0 {
+		return ""
+	}
+	sum := sha256.Sum256(certs[0].Raw)
+	return hex.EncodeToString(sum[:])
+}

client-go/pair_code_linux_test.go

@@ -0,0 +1,626 @@
+//go:build linux
+
+// The pairing code a Cloud Host's card hands out (pair_code.go): one string
+// carrying the token, the enroll address and the Host CA's fingerprint, and
+// the question a local machine asks before it serves a second Host
+// (pair_terminal.go).
+//
+// Uses the fixtures of local_host_linux_test.go and local_host_tcp_linux_test.go
+// (newTestCA, pairingBox, startTCPEnrollHost, homeToken), so it carries the same
+// build tag.
+
+package main
+
+import (
+	"context"
+	"crypto/ecdsa"
+	"crypto/elliptic"
+	"crypto/rand"
+	"crypto/sha256"
+	"crypto/tls"
+	"crypto/x509"
+	"crypto/x509/pkix"
+	"encoding/base64"
+	"encoding/hex"
+	"encoding/json"
+	"errors"
+	"fmt"
+	"io"
+	"math/big"
+	"net"
+	"os"
+	"os/exec"
+	"path/filepath"
+	"strings"
+	"syscall"
+	"testing"
+	"time"
+)
+
+// makePairCode builds a code the way a Host's card does: skp_ and base64url,
+// no padding, of the JSON object fields.
+func makePairCode(t *testing.T, fields map[string]any) string {
+	t.Helper()
+	raw, err := json.Marshal(fields)
+	if err != nil {
+		t.Fatal(err)
+	}
+	return pairCodePrefix + base64.RawURLEncoding.EncodeToString(raw)
+}
+
+func pairCodeFingerprint(ca *testCA) string {
+	sum := sha256.Sum256(ca.cert.Raw)
+	return hex.EncodeToString(sum[:])
+}
+
+// chainWithCA is the enroll port's certificate as a Host from this release
+// serves it: the leaf, then the CA.
+func chainWithCA(t *testing.T, ca *testCA) tls.Certificate {
+	t.Helper()
+	c := ca.serverCert(t, tcpServerName)
+	c.Certificate = append(c.Certificate, ca.cert.Raw)
+	return c
+}
+
+func goodCodeFields(url, fp string) map[string]any {
+	return map[string]any{"v": 1, "u": url, "ca": fp, "t": homeToken()}
+}
+
+// ── decoding ────────────────────────────────────────────────────────────────
+
+func TestAPairingCodeDecodes(t *testing.T) {
+	fp := strings.Repeat("ab", 32)
+	code := makePairCode(t, goodCodeFields("https://maple.example-id.cloud.example:8810/v1/local/redeem", fp))
+	pc, err := decodePairCode(code)
+	if err != nil {
+		t.Fatal(err)
+	}
+	if pc.RedeemURL != "https://maple.example-id.cloud.example:8810/v1/local/redeem" || pc.CASHA256 != fp || pc.Token != homeToken() {
+		t.Fatalf("decoded: %+v", pc)
+	}
+	token, opts, err := pairOptsFor(code, "", "", false)
+	if err != nil || token != homeToken() || opts.redeemURL != pc.RedeemURL || opts.caSHA256 != fp || opts.hostCAFile != "" || opts.askSecond == nil {
+		t.Fatalf("pair's options from a code: %q %+v %v", token, opts, err)
+	}
+	if _, _, err := pairOptsFor(code, "", "host-ca.pem", false); err == nil {
+		t.Fatal("a code carries its own certificate: --host-ca beside it must be refused")
+	}
+	if tok, opts, err := pairOptsFor(homeToken(), "", "", false); err != nil || tok != homeToken() || opts.caSHA256 != "" {
+		t.Fatalf("a bare token passes through as it was: %q %+v %v", tok, opts, err)
+	}
+}
+
+// A code this bastion cannot read is refused with what was wrong, never
+// with its content: a log of a failed install must not hold the token.
+func TestAPairingCodeIsReadStrictly(t *testing.T) {
+	fp := strings.Repeat("0f", 32)
+	u := "https://maple.example-id.cloud.example:8810/v1/local/redeem"
+	with := func(edit func(m map[string]any)) string {
+		m := goodCodeFields(u, fp)
+		edit(m)
+		return makePairCode(t, m)
+	}
+	for name, code := range map[string]string{
+		"garbled":           "skp_%%%not-base64%%%",
+		"not JSON":          pairCodePrefix + base64.RawURLEncoding.EncodeToString([]byte("secret-x home")),
+		"wrong version":     with(func(m map[string]any) { m["v"] = 2 }),
+		"version as text":   with(func(m map[string]any) { m["v"] = "1" }),
+		"extra key":         with(func(m map[string]any) { m["x"] = "y" }),
+		"missing key":       with(func(m map[string]any) { delete(m, "ca") }),
+		"another key":       with(func(m map[string]any) { delete(m, "t"); m["token"] = homeToken() }),
+		"http address":      with(func(m map[string]any) { m["u"] = "http://maple.example-id.cloud.example:8810/v1/local/redeem" }),
+		"address with user": with(func(m map[string]any) { m["u"] = "https://a@maple.example-id.cloud.example/v1/local/redeem" }),
+		"short fingerprint": with(func(m map[string]any) { m["ca"] = fp[:63] }),
+		"upper fingerprint": with(func(m map[string]any) { m["ca"] = strings.ToUpper(fp) }),
+		"not hex":           with(func(m map[string]any) { m["ca"] = strings.Repeat("zz", 32) }),
+		"no skb_ token":     with(func(m map[string]any) { m["t"] = "secret-x" }),
+		"malformed token":   with(func(m map[string]any) { m["t"] = "skb_bm9kb3Q" }), // base64url("nodot")
+	} {
+		_, err := decodePairCode(code)
+		if err == nil {
+			t.Errorf("%s: refused nothing", name)
+			continue
+		}
+		if strings.Contains(err.Error(), "secret-x") || strings.Contains(err.Error(), homeToken()) {
+			t.Errorf("%s: the refusal repeats the token: %v", name, err)
+		}
+	}
+	_, err := decodePairCode(with(func(m map[string]any) { m["v"] = 2 }))
+	if err == nil || !strings.Contains(err.Error(), "update the bastion") {
+		t.Fatalf("a newer code says to update the bastion: %v", err)
+	}
+}
+
+// ── the pinned CA ───────────────────────────────────────────────────────────
+
+// SECURITY: the CA is taken from the enroll port's chain only when its
+// SHA-256 is the code's, and the port's own certificate must verify under it
+// for tcpServerName. A chain without the CA, another CA, or a leaf another CA
+// signed are refused before the token is spent, and nothing is saved.
+func TestAPairingCodePinsTheHostCAByFingerprint(t *testing.T) {
+	ca := newTestCA(t, "maple host CA")
+	impostor := newTestCA(t, "impostor")
+	leafByImpostor := impostor.serverCert(t, tcpServerName)
+	leafByImpostor.Certificate = append(leafByImpostor.Certificate, ca.cert.Raw)
+	for name, c := range map[string]struct {
+		serve tls.Certificate
+		fp    string
+		want  string
+	}{
+		"no CA in the chain":       {ca.serverCert(t, tcpServerName), pairCodeFingerprint(ca), "did not present"},
+		"another CA in the chain":  {chainWithCA(t, impostor), pairCodeFingerprint(ca), "other than"},
+		"another fingerprint":      {chainWithCA(t, ca), pairCodeFingerprint(impostor), "other than"},
+		"a leaf another CA signed": {leafByImpostor, pairCodeFingerprint(ca), "not signed by"},
+		"the CA, under another name": {func() tls.Certificate {
+			c := ca.serverCert(t, "maple.example")
+			c.Certificate = append(c.Certificate, ca.cert.Raw)
+			return c
+		}(), pairCodeFingerprint(ca), "not signed by"},
+	} {
+		t.Run(name, func(t *testing.T) {
+			pairingBox(t)
+			h := startTCPEnrollHost(t, ca, c.serve, "127.0.0.1:18821")
+			token, opts, err := pairOptsFor(makePairCode(t, goodCodeFields(h.url, c.fp)), "", "", false)
+			if err != nil {
+				t.Fatal(err)
+			}
+			_, _, err = pairWith(token, opts)
+			if err == nil || !strings.Contains(err.Error(), c.want) {
+				t.Fatalf("want a refusal naming %q, got %v", c.want, err)
+			}
+			if h.hits.Load() != 0 {
+				t.Fatal("the token went to an enroll port whose CA was never checked")
+			}
+			if cfgs, _ := loadPairings(); len(cfgs) != 0 {
+				t.Fatalf("a refused pairing saved %d pairings", len(cfgs))
+			}
+		})
+	}
+}
+
+// A good code pairs exactly as --redeem-url u --host-ca <that CA> t does: the
+// same TCP pairing, the same CA pinned.
+func TestAPairingCodePairsAsTheHostCAFileDoes(t *testing.T) {
+	pairingBox(t)
+	ca := newTestCA(t, "maple host CA")
+	h := startTCPEnrollHost(t, ca, chainWithCA(t, ca), "127.0.0.1:18822")
+	token, opts, err := pairOptsFor(makePairCode(t, goodCodeFields(h.url, pairCodeFingerprint(ca))), "", "", false)
+	if err != nil {
+		t.Fatal(err)
+	}
+	cfg, _, err := pairWith(token, opts)
+	if err != nil {
+		t.Fatal(err)
+	}
+	if !cfg.tcpTransport() || !sameCAs(cfg.CACert, ca.pem) || cfg.LaneAddr != "127.0.0.1:18822" || cfg.HostName != "home.example.test" {
+		t.Fatalf("the pairing: transport %q lane %q host %q", cfg.Transport, cfg.LaneAddr, cfg.HostName)
+	}
+	h.mu.Lock()
+	req, sni := h.last, h.sni
+	h.mu.Unlock()
+	if req.Secret != "secret-x" || req.Handle != "home" || sni != tcpServerName {
+		t.Fatalf("the redeem is today's: secret %q handle %q sni %q", req.Secret, req.Handle, sni)
+	}
+
+	// The same code again: already paired with this Host, nothing changed,
+	// and the error is the one `pair` exits 3 on.
+	before, _ := os.ReadFile(filepath.Join(mustPairingsDir(t), "home.example.test.json"))
+	token, opts, _ = pairOptsFor(makePairCode(t, goodCodeFields(h.url, pairCodeFingerprint(ca))), "", "", false)
+	_, _, err = pairWith(token, opts)
+	var already *alreadyPairedError
+	if !errors.As(err, &already) {
+		t.Fatalf("pairing the same Host again must be alreadyPairedError (exit %d), got %v", pairExitAlreadyPaired, err)
+	}
+	after, _ := os.ReadFile(filepath.Join(mustPairingsDir(t), "home.example.test.json"))
+	if string(before) != string(after) || h.hits.Load() != 1 {
+		t.Fatal("an already-paired Host must change nothing and spend no token")
+	}
+
+	// Another Host of the same name (Cloud names repeat): a different CA, so
+	// never "already connected".
+	other := newTestCA(t, "another maple")
+	h2 := startTCPEnrollHost(t, other, chainWithCA(t, other), "127.0.0.1:18823")
+	token, opts, _ = pairOptsFor(makePairCode(t, goodCodeFields(h2.url, pairCodeFingerprint(other))), "", "", false)
+	_, _, err = pairWith(token, opts)
+	if err == nil || errors.As(err, &already) || !strings.Contains(err.Error(), "different Host named") {
+		t.Fatalf("a same-named Host under another CA is a plain refusal, not exit 3: %v", err)
+	}
+}
+
+func mustPairingsDir(t *testing.T) string {
+	t.Helper()
+	d, err := pairingsDir()
+	if err != nil {
+		t.Fatal(err)
+	}
+	return d
+}
+
+// ── an enroll port that does not answer ─────────────────────────────────────
+
+// A Cloud Host's pairing port drops every address but the one the card opened
+// it to. A pair from elsewhere says so within pairAnswerTimeout, in plain
+// words, instead of waiting for the system's connect timeout. Both the code
+// and --host-ca paths.
+func TestAnEnrollPortThatDoesNotAnswerNamesThePairingWindow(t *testing.T) {
+	pairingBox(t)
+	oldTimeout, oldDial := pairAnswerTimeout, pairDial
+	t.Cleanup(func() { pairAnswerTimeout, pairDial = oldTimeout, oldDial })
+	pairAnswerTimeout = 150 * time.Millisecond
+	pairDial = func(ctx context.Context, _, _ string) (net.Conn, error) {
+		<-ctx.Done()
+		return nil, ctx.Err()
+	}
+	u := "https://maple.example-id.cloud.example:8810/v1/local/redeem"
+	ca := newTestCA(t, "maple host CA")
+	check := func(name string, err error, took time.Duration) {
+		t.Helper()
+		var we *pairWindowError
+		if !errors.As(err, &we) {
+			t.Fatalf("%s: want the pairing-window message, got %v", name, err)
+		}
+		msg := err.Error()
+		if !strings.Contains(msg, "maple.example-id.cloud.example's pairing port didn't answer") ||
+			!strings.Contains(msg, "15 minutes") || !strings.Contains(msg, "another network") || !strings.Contains(msg, "Nothing was paired") {
+			t.Fatalf("%s: the message: %s", name, msg)
+		}
+		if took > 2*time.Second {
+			t.Fatalf("%s: took %s, the timeout is %s", name, took, pairAnswerTimeout)
+		}
+	}
+	start := time.Now()
+	token, opts, _ := pairOptsFor(makePairCode(t, goodCodeFields(u, pairCodeFingerprint(ca))), "", "", false)
+	_, _, err := pairWith(token, opts)
+	check("pairing code", err, time.Since(start))
+
+	start = time.Now()
+	_, _, err = pairWithTokenVia(homeToken(), u, writeCA(t, ca), false, false)
+	check("--host-ca", err, time.Since(start))
+}
+
+// ── a local machine that already serves a Host ──────────────────────────────
+
+// fakeTerminal stands in a person at this machine: their answer, and what
+// the question said. answer "" with noTerm set is a run with no terminal.
+type fakeTerminal struct {
+	answer string
+	noTerm bool
+	asked  strings.Builder
+	opened int
+}
+
+func (f *fakeTerminal) use(t *testing.T) {
+	t.Helper()
+	old := openTerminal
+	t.Cleanup(func() { openTerminal = old })
+	openTerminal = func() (io.Reader, io.Writer, func(), error) {
+		f.opened++
+		if f.noTerm {
+			return nil, nil, nil, errNoTerminal
+		}
+		return strings.NewReader(f.answer), &f.asked, func() {}, nil
+	}
+}
+
+func otherToken() string { return "skb_b3RoZXIuc2VjcmV0LXk" } // base64url("other.secret-y")
+
+// SECURITY: a local machine that serves a Host adds another only on a yes
+// typed at this machine's terminal. No terminal, or any answer but y or yes,
+// refuses before the token is spent, and the first pairing is untouched.
+// Every caller but `pair` (claim-anchor, the pairing op) keeps the old
+// refusal: it has no person to ask.
+func TestALocalMachineAddsASecondHostOnlyOnAYesTypedHere(t *testing.T) {
+	pairingBox(t)
+	ca := newTestCA(t, "home host CA")
+	home := startTCPEnrollHost(t, ca, ca.serverCert(t, tcpServerName), "127.0.0.1:18831")
+	if _, _, err := pairWithTokenVia(homeToken(), home.url, writeCA(t, ca), false, false); err != nil {
+		t.Fatal(err)
+	}
+	first, _ := os.ReadFile(filepath.Join(mustPairingsDir(t), "home.example.test.json"))
+
+	otherCA := newTestCA(t, "other host CA")
+	other := startTCPEnrollHost(t, otherCA, chainWithCA(t, otherCA), "127.0.0.1:18832")
+	other.set(func(h *tcpEnrollHost) {
+		h.edit = func(ans map[string]any) { ans["host_handle"], ans["host_name"] = "other", "other.example.test" }
+	})
+	code := makePairCode(t, map[string]any{"v": 1, "u": other.url, "ca": pairCodeFingerprint(otherCA), "t": otherToken()})
+	pairOther := func() error {
+		token, opts, err := pairOptsFor(code, "", "", false)
+		if err != nil {
+			t.Fatal(err)
+		}
+		_, _, err = pairWith(token, opts)
+		return err
+	}
+	untouched := func(why string) {
+		t.Helper()
+		now, _ := os.ReadFile(filepath.Join(mustPairingsDir(t), "home.example.test.json"))
+		cfgs, _ := loadPairings()
+		if string(now) != string(first) {
+			t.Fatalf("%s: the first pairing changed", why)
+		}
+		if why != "yes" && (len(cfgs) != 1 || other.hits.Load() != 0) {
+			t.Fatalf("%s: %d pairings, %d redeems", why, len(cfgs), other.hits.Load())
+		}
+	}
+
+	// No terminal: refused, and it says where to run it instead.
+	ft := &fakeTerminal{noTerm: true}
+	ft.use(t)
+	if err := pairOther(); err == nil || !strings.Contains(err.Error(), "terminal window on this computer") {
+		t.Fatalf("no terminal must refuse in plain words: %v", err)
+	}
+	untouched("no terminal")
+
+	// Anything but y or yes.
+	for _, a := range []string{"\n", "n\n", "no\n", "yess\n", "sure\n", ""} {
+		ft := &fakeTerminal{answer: a}
+		ft.use(t)
+		if err := pairOther(); err == nil || !strings.Contains(err.Error(), "stays the only Host") {
+			t.Fatalf("answer %q must refuse: %v", a, err)
+		}
+		if !strings.Contains(ft.asked.String(), "already serves your Host home.example.test. Add other as well?") {
+			t.Fatalf("the question: %q", ft.asked.String())
+		}
+		untouched("answer " + a)
+	}
+
+	// The callers with no person to ask keep the refusal, and ask nobody.
+	ft = &fakeTerminal{answer: "y\n"}
+	ft.use(t)
+	var second *localSecondHostError
+	if _, _, err := pairWithTokenVia(otherToken(), other.url, writeCA(t, otherCA), false, false); !errors.As(err, &second) {
+		t.Fatalf("pairWithTokenVia (no person to ask) must keep the refusal: %v", err)
+	}
+	if ft.opened != 0 {
+		t.Fatal("a caller with no person to ask opened the terminal")
+	}
+	untouched("no asker")
+
+	// A typed yes adds it beside the first.
+	ft = &fakeTerminal{answer: "Yes\n"}
+	ft.use(t)
+	if err := pairOther(); err != nil {
+		t.Fatal(err)
+	}
+	cfgs, _ := loadPairings()
+	if len(cfgs) != 2 || pairingFor(cfgs, "other.example.test") == nil {
+		t.Fatalf("after yes: %d pairings", len(cfgs))
+	}
+	untouched("yes")
+}
+
+// secondHostStdinChild set to 1 makes this test binary the child of
+// TestTheSecondHostAnswerIsNeverReadFromStandardInput.
+const secondHostStdinChild = "PRIVATAE_TEST_SECOND_HOST_STDIN_CHILD"
+
+// SECURITY: the answer to the second-Host question comes from the controlling
+// terminal, never from standard input. The installers hand the pairing code to
+// `pair -` on standard input, so a "y" piped in after the code must not add a
+// Host. The real openTerminal runs in a child with no controlling terminal (a
+// session of its own) and "y" waiting on its standard input: it must find no
+// terminal, and leave standard input unread.
+func TestTheSecondHostAnswerIsNeverReadFromStandardInput(t *testing.T) {
+	if os.Getenv(secondHostStdinChild) == "1" {
+		yes, err := confirmAddHost("home.example.test", "other")
+		rest, _ := io.ReadAll(os.Stdin)
+		fmt.Printf("child: yes=%v refused=%v stdin-left=%q\n", yes, err != nil && strings.Contains(err.Error(), "no terminal"), rest)
+		os.Exit(0)
+	}
+	self, err := os.Executable()
+	if err != nil {
+		t.Fatal(err)
+	}
+	cmd := exec.Command(self, "-test.run=^TestTheSecondHostAnswerIsNeverReadFromStandardInput$")
+	cmd.Env = append(os.Environ(), secondHostStdinChild+"=1")
+	cmd.Stdin = strings.NewReader("y\n")
+	cmd.SysProcAttr = &syscall.SysProcAttr{Setsid: true}
+	out, err := cmd.CombinedOutput()
+	if err != nil {
+		t.Fatalf("the child: %v\n%s", err, out)
+	}
+	if !strings.Contains(string(out), `child: yes=false refused=true stdin-left="y\n"`) {
+		t.Fatalf("a y on standard input must neither answer the question nor be read: %s", out)
+	}
+}
+
+// The refusal names this system's own way to a networked bastion, and says
+// that the Host already here would have to be paired again.
+func TestTheLocalRefusalSaysWhatANetworkedReinstallCosts(t *testing.T) {
+	msg := localOneHostRefusal("home.example.test")
+	if !strings.Contains(msg, "install.sh --networked") || strings.Contains(msg, "install.ps1") {
+		t.Fatalf("on linux it names install.sh: %s", msg)
+	}
+	if !strings.Contains(msg, "home.example.test has to be paired with it again") || !strings.Contains(msg, "answer yes at this computer's terminal") {
+		t.Fatalf("the refusal: %s", msg)
+	}
+}
+
+// ── what the Host's card actually makes ─────────────────────────────────────
+
+// Made by the C-Series Host's own pairing_code (bastion_enroll.py) from the CA
+// below and an invented token, for an invented address: compact JSON with the
+// keys v, u, ca and t in base64url without padding. The bastion must read
+// exactly that, and the fingerprint must be the one caSHA256 computes from
+// the same CA, or a real code would never pin.
+const hostMadePairCode = "skp_eyJ2IjoxLCJ1IjoiaHR0cHM6Ly9tYXBsZS5leGFtcGxlLWlkLmNsb3VkLmV4YW1wbGU6ODgxMC92MS9sb2NhbC9yZWRlZW0iLCJjYSI6IjcyMzNkOWU4ODU5MzIyZjE1YTJiNmMzYWIyMmZiNjMxNGI4M2I0Njg2ZmNhYmZiYjRmNGU1NDE5NDA1MTFkMDciLCJ0Ijoic2tiX2JXRndiR1V1YzJWamNtVjBMV2x1ZG1WdWRHVmtMVEF3TURFIn0"
+
+const hostMadePairCodeCA = `-----BEGIN CERTIFICATE-----
+MIIBTTCB9KADAgECAgIQkjAKBggqhkjOPQQDAjAjMSEwHwYDVQQDDBhleGFtcGxl
+IGludmVudGVkIGhvc3QgQ0EwIBcNMjYwMTAxMDAwMDAwWhgPMjEyNTEyMDgwMDAw
+MDBaMCMxITAfBgNVBAMMGGV4YW1wbGUgaW52ZW50ZWQgaG9zdCBDQTBZMBMGByqG
+SM49AgEGCCqGSM49AwEHA0IABA32JMrh4sMMLvNNoSBq5FgXFgHd/2n71Qk9ayje
+Kj9rdt+Q3CFYWgtCqFHc6ZLUfXexKkdWvnET3px2hGqZWbKjFjAUMBIGA1UdEwEB
+/wQIMAYBAf8CAQAwCgYIKoZIzj0EAwIDSAAwRQIhAIQ6sKtiqxcAQTPq7+toiEl0
+qrWb4CKKB2UtvcQoC9YwAiBYGKbmvG9ZszE8X7uKUGexjP9x6lDOwqfmnLoruuVg
+Kg==
+-----END CERTIFICATE-----
+`
+
+func TestACodeTheHostMadeDecodesAndPins(t *testing.T) {
+	pc, err := decodePairCode(hostMadePairCode)
+	if err != nil {
+		t.Fatal(err)
+	}
+	if pc.RedeemURL != "https://maple.example-id.cloud.example:8810/v1/local/redeem" ||
+		pc.Token != "skb_bWFwbGUuc2VjcmV0LWludmVudGVkLTAwMDE" { // base64url("maple.secret-invented-0001")
+		t.Fatalf("decoded: %+v", pc)
+	}
+	if got := caSHA256(hostMadePairCodeCA); got != pc.CASHA256 {
+		t.Fatalf("the Host's fingerprint %s is not caSHA256 of its CA (%s)", pc.CASHA256, got)
+	}
+	if h, _, err := decodeToken(pc.Token); err != nil || h != "maple" {
+		t.Fatalf("the token's handle: %q %v", h, err)
+	}
+}
+
+// SECURITY: a key given twice is an extra key. A map would keep only the
+// last, so two codes that differ in which token they carry could both read as
+// "exactly v, u, ca and t".
+func TestAPairingCodeWithAKeyGivenTwiceIsRefused(t *testing.T) {
+	fp := strings.Repeat("0f", 32)
+	u := "https://maple.example-id.cloud.example:8810/v1/local/redeem"
+	raw := `{"v":1,"u":"` + u + `","ca":"` + fp + `","t":"` + otherToken() + `","t":"` + homeToken() + `"}`
+	if _, err := decodePairCode(pairCodePrefix + base64.RawURLEncoding.EncodeToString([]byte(raw))); err == nil {
+		t.Fatal("a code naming t twice was read")
+	}
+	once := `{"v":1,"u":"` + u + `","ca":"` + fp + `","t":"` + homeToken() + `"}`
+	if _, err := decodePairCode(pairCodePrefix + base64.RawURLEncoding.EncodeToString([]byte(once))); err != nil {
+		t.Fatalf("the same code with t once: %v", err)
+	}
+}
+
+// pinnedChainCert is a certificate for the pinned-chain cases: signed by
+// parent (self-signed when parent is nil), a CA or not, valid from nb to na.
+func pinnedChainCert(t *testing.T, cn string, isCA bool, nb, na time.Time, parent *x509.Certificate, parentKey *ecdsa.PrivateKey, dns ...string) (*x509.Certificate, *ecdsa.PrivateKey) {
+	t.Helper()
+	key, _ := ecdsa.GenerateKey(elliptic.P256(), rand.Reader)
+	tmpl := &x509.Certificate{SerialNumber: big.NewInt(time.Now().UnixNano()), Subject: pkix.Name{CommonName: cn},
+		NotBefore: nb, NotAfter: na, DNSNames: dns, BasicConstraintsValid: true, IsCA: isCA}
+	if isCA {
+		tmpl.KeyUsage = x509.KeyUsageCertSign | x509.KeyUsageDigitalSignature
+	} else {
+		tmpl.KeyUsage, tmpl.ExtKeyUsage = x509.KeyUsageDigitalSignature, []x509.ExtKeyUsage{x509.ExtKeyUsageServerAuth}
+	}
+	signer, signKey := tmpl, key
+	if parent != nil {
+		signer, signKey = parent, parentKey
+	}
+	der, err := x509.CreateCertificate(rand.Reader, tmpl, signer, &key.PublicKey, signKey)
+	if err != nil {
+		t.Fatal(err)
+	}
+	c, _ := x509.ParseCertificate(der)
+	return c, key
+}
+
+// SECURITY: the cases of the pinned chain the TLS tests do not reach. A
+// certificate with the code's fingerprint that is not a CA, and a CA that has
+// expired, are refused; the pinned CA anywhere after the leaf, beside other
+// certificates, is the one returned.
+func TestThePinnedChainTakesOnlyAValidCAWithTheFingerprint(t *testing.T) {
+	now := time.Now()
+	fpOf := func(c *x509.Certificate) string { s := sha256.Sum256(c.Raw); return hex.EncodeToString(s[:]) }
+
+	ca, caKey := pinnedChainCert(t, "maple host CA", true, now.Add(-time.Hour), now.Add(24*time.Hour), nil, nil)
+	leaf, _ := pinnedChainCert(t, "leaf", false, now.Add(-time.Hour), now.Add(time.Hour), ca, caKey, tcpServerName)
+	other, _ := pinnedChainCert(t, "another CA", true, now.Add(-time.Hour), now.Add(24*time.Hour), nil, nil)
+	got, err := verifyPinnedChain([]*x509.Certificate{leaf, other, ca}, fpOf(ca))
+	if err != nil || caSHA256(got) != fpOf(ca) {
+		t.Fatalf("the pinned CA after another certificate: %v", err)
+	}
+
+	// A self-signed certificate that is not a CA, signing the leaf.
+	notCA, notCAKey := pinnedChainCert(t, "not a CA", false, now.Add(-time.Hour), now.Add(24*time.Hour), nil, nil)
+	leaf2, _ := pinnedChainCert(t, "leaf", false, now.Add(-time.Hour), now.Add(time.Hour), notCA, notCAKey, tcpServerName)
+	if _, err := verifyPinnedChain([]*x509.Certificate{leaf2, notCA}, fpOf(notCA)); err == nil {
+		t.Fatal("a certificate with the fingerprint that is not a CA was pinned")
+	}
+
+	// An expired CA, with a leaf it signed that is still in its dates.
+	old, oldKey := pinnedChainCert(t, "expired host CA", true, now.Add(-48*time.Hour), now.Add(-time.Hour), nil, nil)
+	leaf3, _ := pinnedChainCert(t, "leaf", false, now.Add(-2*time.Hour), now.Add(time.Hour), old, oldKey, tcpServerName)
+	if _, err := verifyPinnedChain([]*x509.Certificate{leaf3, old}, fpOf(old)); err == nil {
+		t.Fatal("an expired CA was pinned")
+	}
+
+	if _, err := verifyPinnedChain([]*x509.Certificate{leaf}, fpOf(ca)); err == nil {
+		t.Fatal("a chain of the leaf alone was accepted")
+	}
+}
+
+// Exit 3 means the same Host, so the same CA, on every TCP pairing: a
+// --host-ca pair to a Host of a name already paired here under another CA is
+// a plain failure, as the pairing code's is.
+func TestHostCAFileWithASameNamedHostUnderAnotherCAIsNotAlreadyPaired(t *testing.T) {
+	pairingBox(t)
+	ca := newTestCA(t, "home host CA")
+	h := startTCPEnrollHost(t, ca, ca.serverCert(t, tcpServerName), "127.0.0.1:18841")
+	if _, _, err := pairWithTokenVia(homeToken(), h.url, writeCA(t, ca), false, false); err != nil {
+		t.Fatal(err)
+	}
+	var already *alreadyPairedError
+	if _, _, err := pairWithTokenVia(homeToken(), h.url, writeCA(t, ca), false, false); !errors.As(err, &already) {
+		t.Fatalf("the same Host under its own CA is already paired (exit 3): %v", err)
+	}
+	other := newTestCA(t, "another home")
+	h2 := startTCPEnrollHost(t, other, other.serverCert(t, tcpServerName), "127.0.0.1:18842")
+	_, _, err := pairWithTokenVia(homeToken(), h2.url, writeCA(t, other), false, false)
+	if err == nil || errors.As(err, &already) || !strings.Contains(err.Error(), "different Host named") {
+		t.Fatalf("a same-named Host under another CA is a plain refusal, not exit 3: %v", err)
+	}
+	if h2.hits.Load() != 0 {
+		t.Fatal("the refusal spent the other Host's token")
+	}
+}
+
+// SECURITY: the name in the question is the token's handle, which whoever
+// made the token chose. A control character or escape sequence in it reaches
+// the person's screen escaped, so it cannot rewrite the question.
+func TestTheSecondHostQuestionEscapesTheTokensName(t *testing.T) {
+	ft := &fakeTerminal{answer: "n\n"}
+	ft.use(t)
+	if _, err := confirmAddHost("home.example.test", "evil\r\x1b[2K\x1b[1Ainnocent"); err != nil {
+		t.Fatal(err)
+	}
+	q := ft.asked.String()
+	if strings.ContainsAny(q, "\x1b\r") {
+		t.Fatalf("the question carries the handle's control bytes raw: %q", q)
+	}
+	if !strings.Contains(q, `Add "evil\r\x1b[2K\x1b[1Ainnocent" as well?`) {
+		t.Fatalf("the question: %q", q)
+	}
+	ft = &fakeTerminal{answer: "n\n"}
+	ft.use(t)
+	if _, err := confirmAddHost("home.example.test", "maple"); err != nil || !strings.Contains(ft.asked.String(), "Add maple as well?") {
+		t.Fatalf("a plain name is shown as it is: %q %v", ft.asked.String(), err)
+	}
+}
+
+// The name the redeem answers with is checked again after the redeem (the
+// token's handle can differ from it). There too, the same name under another
+// CA is a plain failure, never exit 3.
+func TestARedeemAnsweringAPairedNameUnderAnotherCAIsNotAlreadyPaired(t *testing.T) {
+	pairingBox(t)
+	ca := newTestCA(t, "home host CA")
+	h := startTCPEnrollHost(t, ca, ca.serverCert(t, tcpServerName), "127.0.0.1:18843")
+	if _, _, err := pairWithTokenVia(homeToken(), h.url, writeCA(t, ca), false, false); err != nil {
+		t.Fatal(err)
+	}
+	other := newTestCA(t, "another home")
+	h2 := startTCPEnrollHost(t, other, chainWithCA(t, other), "127.0.0.1:18844")
+	// otherToken's handle is "other"; the Host answers home.example.test.
+	token, opts, err := pairOptsFor(makePairCode(t, map[string]any{"v": 1, "u": h2.url, "ca": pairCodeFingerprint(other), "t": otherToken()}), "", "", false)
+	if err != nil {
+		t.Fatal(err)
+	}
+	opts.askSecond = func(string, string) (bool, error) { return true, nil }
+	_, _, err = pairWith(token, opts)
+	var already *alreadyPairedError
+	if err == nil || errors.As(err, &already) || !strings.Contains(err.Error(), "different Host named home.example.test") {
+		t.Fatalf("a redeem naming a paired Host under another CA is a plain refusal, not exit 3: %v", err)
+	}
+	if cfgs, _ := loadPairings(); len(cfgs) != 1 {
+		t.Fatalf("%d pairings after the refusal", len(cfgs))
+	}
+}

client-go/pair_tcp.go

@@ -149,11 +149,19 @@ func redeemOverTCP(u *url.URL, caPEM string, body []byte) (tcpRedeemResp, error)
 	if err != nil {
 		return rr, fmt.Errorf("--host-ca: %w", err)
 	}
+	// The dial is dialEnrollPort's: an enroll port that does not answer in
+	// pairAnswerTimeout gets the pairing window's plain message, not a wait
+	// for the system's connect timeout.
 	httpc := &http.Client{Timeout: 30 * time.Second, Transport: &http.Transport{
 		Proxy: nil, TLSClientConfig: tc, ForceAttemptHTTP2: false,
+		DialContext: func(ctx context.Context, _, _ string) (net.Conn, error) { return dialEnrollPort(ctx, u) },
 	}, CheckRedirect: func(*http.Request, []*http.Request) error { return http.ErrUseLastResponse }}
 	resp, err := httpc.Post(u.String(), "application/json", bytes.NewReader(body))
 	if err != nil {
+		var we *pairWindowError
+		if errors.As(err, &we) {
+			return rr, we
+		}
 		return rr, fmt.Errorf("redeem: %w", err)
 	}
 	defer resp.Body.Close()

client-go/pair_terminal.go

@@ -0,0 +1,66 @@
+package main
+
+// pair_terminal.go: the one question `pair` asks a person, on a local machine
+// that already serves a Host: whether to add another.
+//
+// A local bastion used to serve one Host, full stop, because on a single-user
+// machine a second Host appearing meant someone else had got a token onto the
+// box. A person who uses two Hosts (a Cloud machine beside the platform one)
+// could not pair the second at all. Now the second is added when the person at
+// this machine says so, and only then: the answer is read from the controlling
+// terminal, never from standard input, so a token piped in by a script or an
+// installer (which feeds the pairing code through standard input) cannot add a
+// Host by itself. With no terminal there is nobody to ask, and the pair is
+// refused.
+
+import (
+	"bufio"
+	"errors"
+	"fmt"
+	"io"
+	"strconv"
+	"strings"
+)
+
+// errNoTerminal: this process has no controlling terminal to ask on.
+var errNoTerminal = errors.New("no terminal")
+
+// openTerminal opens the controlling terminal for one question: a reader for
+// the answer, a writer for the question, and a close. A variable so a test can
+// stand in a person; nothing else assigns it.
+var openTerminal = openControllingTerminal
+
+// terminalSafeName is a Host name as the question shows it. newHost is the
+// handle the token carries, which nothing has checked yet: whoever made the
+// token chose it, and a control character or an escape sequence in it could
+// rewrite the question on the person's screen. A plain host name is shown as
+// it is; anything else is quoted, every such byte escaped.
+func terminalSafeName(name string) string {
+	if validHostName(name) {
+		return name
+	}
+	return strconv.QuoteToASCII(name)
+}
+
+// confirmAddHost asks whether to add newHost beside serving, the Host this
+// local machine already serves. True only for a typed y or yes.
+func confirmAddHost(serving, newHost string) (bool, error) {
+	in, out, closeTerm, err := openTerminal()
+	if err != nil {
+		return false, fmt.Errorf("this computer already serves your Host %s, and adding another needs a yes typed "+
+			"at this computer, but this run has no terminal to ask in. Run the same command in a terminal "+
+			"window on this computer; nothing was paired", serving)
+	}
+	defer closeTerm()
+	fmt.Fprintf(out, "This computer already serves your Host %s. Add %s as well? It gets a pairing of its own,\n"+
+		"and `privatae-bastion ui` shows what each Host may do here. [y/N] ", terminalSafeName(serving), terminalSafeName(newHost))
+	line, err := bufio.NewReader(io.LimitReader(in, 256)).ReadString('\n')
+	if err != nil && !errors.Is(err, io.EOF) {
+		return false, fmt.Errorf("could not read the answer (%v); nothing was paired", err)
+	}
+	switch strings.ToLower(strings.TrimSpace(line)) {
+	case "y", "yes":
+		return true, nil
+	}
+	return false, nil
+}

client-go/pair_terminal_unix.go

@@ -0,0 +1,19 @@
+//go:build !windows
+
+package main
+
+import (
+	"io"
+	"os"
+)
+
+// openControllingTerminal opens /dev/tty, this process's controlling terminal
+// whatever its standard input is. It fails with no terminal (a service, a
+// pipe from `ssh host cmd` without -t, cron).
+func openControllingTerminal() (io.Reader, io.Writer, func(), error) {
+	f, err := os.OpenFile("/dev/tty", os.O_RDWR, 0)
+	if err != nil {
+		return nil, nil, nil, errNoTerminal
+	}
+	return f, f, func() { _ = f.Close() }, nil
+}

client-go/pair_terminal_windows.go

@@ -0,0 +1,26 @@
+//go:build windows
+
+package main
+
+import (
+	"io"
+	"os"
+)
+
+// openControllingTerminal opens the console this process is attached to,
+// CONIN$ for the answer and CONOUT$ for the question, whatever its standard
+// input is: install.ps1 pipes the pairing code into `pair -`, and the person
+// still answers in the PowerShell window. It fails with no console (a
+// service, a scheduled task with no window).
+func openControllingTerminal() (io.Reader, io.Writer, func(), error) {
+	in, err := os.OpenFile("CONIN$", os.O_RDWR, 0)
+	if err != nil {
+		return nil, nil, nil, errNoTerminal
+	}
+	out, err := os.OpenFile("CONOUT$", os.O_RDWR, 0)
+	if err != nil {
+		_ = in.Close()
+		return nil, nil, nil, errNoTerminal
+	}
+	return in, out, func() { _ = in.Close(); _ = out.Close() }, nil
+}

client-go/service.go

@@ -288,17 +288,40 @@ func serviceArgs(spec harnessSpec) []string {
 
 // serviceOwnerRefusal: on an anchored box a member pairing may not replace or
 // stop a slot another host built. The anchor pairing may (its user is the
-// machine's admin), and an unanchored local box serves one host.
+// machine's admin). A local box has no anchor to be that admin, and serves a
+// second host only on its person's yes (pair_terminal.go); once it serves two,
+// each host changes only the slots it built. With one host there is nobody to
+// keep apart (a host renamed since it built a slot still owns it), and
+// pairings that cannot be read are treated as two.
 func serviceOwnerRefusal(self string, r *serviceRecord) string {
 	if r == nil || r.Owner == "" || r.Owner == self {
 		return ""
 	}
+	if boxMode() == modeLocal {
+		if !localServesSeveralHosts() {
+			return ""
+		}
+		return "refused: slot '" + r.Name + "' was built by " + r.Owner + "; on a local machine that serves several Hosts each changes only the servers it built"
+	}
 	if why := anchorOnly(self, "changing a server another host built"); why != "" {
 		return "refused: slot '" + r.Name + "' was built by " + r.Owner + "; " + why
 	}
 	return ""
 }
 
+// localServesSeveralHosts: this is a local machine that serves more than one
+// Host (the second added on its person's yes, pair_terminal.go), so what one
+// Host built or started here is kept from the others. Pairings that cannot be
+// read count as several. False on a networked machine, whose anchor rule
+// (anchorOnly) keeps its Hosts apart.
+func localServesSeveralHosts() bool {
+	if boxMode() != modeLocal {
+		return false
+	}
+	cfgs, err := loadPairings()
+	return err != nil || len(cfgs) > 1
+}
+
 func serviceFail(res map[string]interface{}, msg string) ([]byte, int) {
 	res["ok"], res["error"] = false, msg
 	b, _ := json.Marshal(res)

client-go/service_test.go

@@ -495,10 +495,24 @@ func TestServiceOwnerRuleOnAnAnchoredBox(t *testing.T) {
 	if why := serviceOwnerRefusal(tMember, &serviceRecord{Name: "forge", Owner: tMember}); why != "" {
 		t.Fatalf("the builder may change its own server: %s", why)
 	}
-	// Local box: one host, no owner rule to apply.
+	// Local box with one host: nobody to keep apart, as before.
 	t.Setenv("XDG_CONFIG_HOME", t.TempDir())
+	if err := (&Config{HostName: tMember, ListenAddr: "127.0.0.1:7878"}).save(); err != nil {
+		t.Fatal(err)
+	}
 	if why := serviceOwnerRefusal(tMember, r); why != "" {
-		t.Fatalf("a local bastion serves one host: %s", why)
+		t.Fatalf("a local machine with one host applies no owner rule: %s", why)
+	}
+	// Local box serving a second host (added on its person's yes): each host
+	// changes only the servers it built.
+	if err := (&Config{HostName: tAnchor, ListenAddr: "127.0.0.1:7879"}).save(); err != nil {
+		t.Fatal(err)
+	}
+	if why := serviceOwnerRefusal(tMember, r); why == "" || !strings.Contains(why, "built by "+tAnchor) {
+		t.Fatalf("on a local machine serving two hosts one must not change the other's server: %q", why)
+	}
+	if why := serviceOwnerRefusal(tMember, &serviceRecord{Name: "forge", Owner: tMember}); why != "" {
+		t.Fatalf("on a local machine a host changes its own server: %s", why)
 	}
 }
 
@@ -852,3 +866,28 @@ func TestSpliceUnixCarriesBothWays(t *testing.T) {
 	}
 	_ = a.Close()
 }
+
+// A coder run on a local machine that serves two Hosts is stopped only by
+// the Host that started it, as a server is changed only by the Host that
+// built it. With one Host there is nobody to keep apart.
+func TestCoderRunOwnerRuleOnALocalBoxServingTwoHosts(t *testing.T) {
+	t.Setenv("XDG_CONFIG_HOME", t.TempDir())
+	if err := (&Config{HostName: tMember, ListenAddr: "127.0.0.1:7878"}).save(); err != nil {
+		t.Fatal(err)
+	}
+	if why := coderOwnerRefusal(tMember, tAnchor); why != "" {
+		t.Fatalf("a local machine with one host applies no owner rule: %s", why)
+	}
+	if err := (&Config{HostName: tAnchor, ListenAddr: "127.0.0.1:7879"}).save(); err != nil {
+		t.Fatal(err)
+	}
+	if why := coderOwnerRefusal(tMember, tAnchor); why == "" || !strings.Contains(why, "started by "+tAnchor) {
+		t.Fatalf("on a local machine serving two hosts one must not stop the other's run: %q", why)
+	}
+	if why := coderOwnerRefusal(tMember, ""); why == "" {
+		t.Fatal("on a local machine serving two hosts a run of unknown owner proves nothing about self")
+	}
+	if why := coderOwnerRefusal(tMember, tMember); why != "" {
+		t.Fatalf("a host stops its own run: %s", why)
+	}
+}

client-go/testdata/install_ps1_pair.ps1

@@ -0,0 +1,58 @@
+# Runs install.ps1's -Pair block against a stand-in bastion, with the Windows
+# cmdlets it calls stood in by functions that log their call. pwsh on Linux:
+#   pwsh -NoProfile -File testdata/install_ps1_pair.ps1 ../deploy/install.ps1
+# Exits 0 when every case holds, and prints the first that does not.
+param([string]$Script)
+$ErrorActionPreference = 'Stop'
+$src = Get-Content -Raw $Script
+$m = [regex]::Match($src, '(?ms)^if \(\$Pair\) \{\r?\n.*?^\}\r?\n')
+if (-not $m.Success) { Write-Output 'FAIL: install.ps1 has no top-level if ($Pair) { … } block'; exit 1 }
+$block = [scriptblock]::Create($m.Value)
+
+$dir = Join-Path ([IO.Path]::GetTempPath()) ([guid]::NewGuid().ToString())
+New-Item -ItemType Directory -Path $dir | Out-Null
+$log = Join-Path $dir 'log'
+$exe = Join-Path $dir 'privatae-bastion'
+Set-Content -Path $exe -Value ("#!/bin/sh`necho ""ARGV `$*"" >> '$log'`n" +
+    "if [ ""`$1"" = pair ]; then sed 's/^/STDIN /' >> '$log'; exit `$FAKE_RC; fi`necho status-ok`n")
+chmod 755 $exe
+
+function Stop-ScheduledTask { $script:calls += 'stop-task' }
+function Start-ScheduledTask { $script:calls += 'start-task' }
+function Restart-Service { $script:calls += 'restart-service' }
+function Start-Process { $script:calls += 'start-process' }
+function Stop-Process { $script:calls += 'stop-process' }
+function Get-Process { @() }
+function Start-Sleep { }
+function Write-Host { param($Object) $script:out += "$Object`n" }
+
+function Run-Case([string]$rc, [bool]$networked) {
+    $script:calls = @(); $script:out = ''
+    if (Test-Path $log) { Remove-Item $log }
+    $env:FAKE_RC = $rc
+    $Pair = 'skp_INVENTEDCODE'; $Networked = $networked
+    $threw = $null
+    try { . $block } catch { $threw = $_.Exception.Message }
+    $l = if (Test-Path $log) { Get-Content -Raw $log } else { '' }
+    return @{ log = $l; calls = ($script:calls -join ','); out = $script:out; threw = $threw }
+}
+function Fail([string]$why) { Write-Output "FAIL: $why"; exit 1 }
+
+$r = Run-Case '0' $false
+if ($r.threw) { Fail "rc 0 threw: $($r.threw)" }
+if ($r.log -notmatch '(?m)^ARGV pair -$' -or $r.log -match 'ARGV .*skp_') { Fail "the code must reach 'pair -' on stdin, never argv: $($r.log)" }
+if ($r.log -notmatch '(?m)^STDIN skp_INVENTEDCODE\r?$') { Fail "pair's stdin: $($r.log)" }
+if ($r.calls -ne 'stop-task,start-task') { Fail "per-user: stop, then start the logon task: $($r.calls)" }
+if ($r.out -notmatch 'This computer is paired\. The bastion is running, and starts again each time you sign in to Windows\.') { Fail "the ending: $($r.out)" }
+
+$r = Run-Case '3' $false
+if ($r.threw -or $r.out -notmatch 'already paired with this Host') { Fail "exit 3 is success: $($r.threw) $($r.out)" }
+
+$r = Run-Case '1' $false
+if (-not $r.threw -or $r.calls -ne '') { Fail "a failed pair must throw before starting anything: $($r.threw) $($r.calls)" }
+
+$r = Run-Case '0' $true
+if ($r.threw -or $r.calls -ne 'restart-service' -or $r.out -notmatch 'Windows service PrivataeBastion') { Fail "networked restarts the service: $($r.threw) $($r.calls)" }
+
+Remove-Item -Recurse -Force $dir
+Write-Output 'ok: install.ps1 -Pair pairs over stdin, treats exit 3 as success, stops on a failure, restarts task or service'

client-go/uisetup.go

@@ -888,7 +888,7 @@ func (s *uiSetup) anchorChoose(w http.ResponseWriter, r *http.Request) {
 			Class:   "bad",
 			Command: setModeCommandHint(),
 			How:     adminHowTo() + ", then claim the anchor.",
-			Why: "This machine is in local mode, where it serves one host and needs no anchor. " +
+			Why: "This machine is in local mode, where it serves only the Hosts you said yes to here and needs no anchor. " +
 				"An anchor only means something on a networked bastion.",
 		})
 		return