feat(ssh): forward vault keys to remote sessions

Scripts/ssh-agent-forwarding-fixture.py

@@ -0,0 +1,115 @@
+#!/usr/bin/env python3
+"""Ephemeral loopback OpenSSH fixture for SSHAgentForwardingWireTests.
+
+Creates fresh keys, three unprivileged sshd instances (destination, second hop,
+and forwarding-denied destination), and a bare Git repository. Never reads or
+changes the user's SSH configuration or authorized_keys. Requires OpenSSH/git.
+Pass --metadata PATH to TEST_RUNNER_TERMIND_AGENT_FORWARDING_FIXTURE for Xcode.
+"""
+import argparse
+import base64
+import getpass
+import hashlib
+import json
+import os
+from pathlib import Path
+import signal
+import socket
+import subprocess
+import tempfile
+import time
+
+
+def run(*args):
+    subprocess.run(args, check=True, stdout=subprocess.DEVNULL)
+
+
+def port():
+    with socket.socket() as sock:
+        sock.bind(("127.0.0.1", 0))
+        return sock.getsockname()[1]
+
+
+def main():
+    parser = argparse.ArgumentParser(description=__doc__)
+    parser.add_argument("--metadata", required=True)
+    args = parser.parse_args()
+    metadata = Path(args.metadata)
+    processes = []
+    logs = []
+    stopped = False
+
+    def stop(*_):
+        nonlocal stopped
+        stopped = True
+
+    signal.signal(signal.SIGTERM, stop)
+    signal.signal(signal.SIGINT, stop)
+    with tempfile.TemporaryDirectory(prefix="termind-agent-wire-") as directory:
+        root = Path(directory)
+        try:
+            for name in ("server", "login", "forwarded"):
+                run("ssh-keygen", "-q", "-t", "ed25519", "-N", "", "-f", str(root / name))
+            (root / "authorized_keys").write_text((root / "login.pub").read_text() + (root / "forwarded.pub").read_text())
+            run("git", "init", "--bare", "--quiet", str(root / "fixture.git"))
+            shell = root / "fixture-shell"
+            shell.write_text('#!/bin/sh\nif [ -n "$SSH_ORIGINAL_COMMAND" ]; then exec /bin/sh -c "$SSH_ORIGINAL_COMMAND"; else exec /bin/sh -i; fi\n')
+            shell.chmod(0o700)
+            ports = [port() for _ in range(3)]
+            for index, listen_port in enumerate(ports):
+                config = root / f"sshd-{index}.conf"
+                config.write_text(f"""Port {listen_port}
+ListenAddress 127.0.0.1
+HostKey {root / 'server'}
+PidFile {root / f'sshd-{index}.pid'}
+AuthorizedKeysFile {root / 'authorized_keys'}
+StrictModes no
+PasswordAuthentication no
+KbdInteractiveAuthentication no
+UsePAM no
+AllowAgentForwarding {'no' if index == 2 else 'yes'}
+AllowTcpForwarding yes
+ForceCommand {shell}
+LogLevel VERBOSE
+""")
+                log = open(root / f"sshd-{index}.log", "w+")
+                logs.append(log)
+                processes.append(subprocess.Popen(["/usr/sbin/sshd", "-D", "-e", "-f", str(config)], stderr=log))
+            time.sleep(1)
+            for process, log in zip(processes, logs):
+                if process.poll() is not None:
+                    log.seek(0)
+                    raise RuntimeError(log.read())
+            blob = base64.b64decode((root / "server.pub").read_text().split()[1])
+            values = {
+                "port": ports[0], "targetPort": ports[1], "deniedPort": ports[2],
+                "username": getpass.getuser(), "loginPrivateKey": (root / "login").read_text(),
+                "forwardedPrivateKey": (root / "forwarded").read_text(),
+                "forwardedPublicKey": (root / "forwarded.pub").read_text(),
+                "fingerprint": "SHA256:" + base64.b64encode(hashlib.sha256(blob).digest()).decode().rstrip("="),
+                "gitPath": str(root / "fixture.git"),
+            }
+            descriptor = os.open(metadata, os.O_WRONLY | os.O_CREAT | os.O_EXCL, 0o600)
+            with os.fdopen(descriptor, "w") as file:
+                json.dump(values, file)
+            print(f"Agent forwarding fixture ready: {metadata}", flush=True)
+            while not stopped:
+                if any(process.poll() is not None for process in processes):
+                    raise RuntimeError("sshd exited unexpectedly")
+                time.sleep(0.2)
+        finally:
+            metadata.unlink(missing_ok=True)
+            for process in processes:
+                process.terminate()
+            for process in processes:
+                try:
+                    process.wait(timeout=3)
+                except subprocess.TimeoutExpired:
+                    process.kill()
+                    process.wait()
+            for log in logs:
+                log.close()
+
+
+if __name__ == "__main__":
+    main()