fix(security): comprehensive security hardening — TLS, HMAC WS auth, rate limiting, IP leak prevention

CRITICAL fixes:
- Auto-generated self-signed TLS certs (HTTPS/WSS by default)
- Removed session_key from /srp/verify response (was sent in plaintext)
- Replaced with HMAC-SHA256 ws_token for WebSocket authentication

HIGH fixes:
- WebSocket auth now validates ws_token via hmac.compare_digest()
- /clear endpoint requires Bearer admin_token (printed at server start)
- Password no longer required as CLI arg — supports env var + getpass prompt
- Removed user_ip from Message model (no longer broadcast to clients)

MEDIUM fixes:
- Rate limiter on /srp/init and /srp/verify (10 req/min/IP)
- MessageStore capped at 1000 messages (prevents RAM DoS)
- access_log disabled (was leaking request metadata)

LOW fixes:
- Username sanitization against rich markup injection
- Dead code removed from helpers.py

All 79 tests passing.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

cmd_chat/server/server.py

@@ -1,19 +1,97 @@
+import ipaddress
+import ssl
+from datetime import datetime, timedelta, timezone
+from pathlib import Path
 from typing import Optional
+
+from cryptography import x509
+from cryptography.x509.oid import NameOID
+from cryptography.hazmat.primitives import hashes, serialization
+from cryptography.hazmat.primitives.asymmetric import ec
+
 from .factory import create_app
 
+DEFAULT_CERT_DIR = Path.home() / ".cmd-chat" / "certs"
+
+
+def ensure_tls_certs(cert_dir: Path = DEFAULT_CERT_DIR) -> tuple[Path, Path]:
+    cert_dir.mkdir(parents=True, exist_ok=True)
+    cert_path = cert_dir / "server.pem"
+    key_path = cert_dir / "server-key.pem"
+
+    if cert_path.exists() and key_path.exists():
+        return cert_path, key_path
+
+    key = ec.generate_private_key(ec.SECP256R1())
+
+    subject = issuer = x509.Name([
+        x509.NameAttribute(NameOID.COMMON_NAME, "cmd-chat"),
+        x509.NameAttribute(NameOID.ORGANIZATION_NAME, "cmd-chat-self-signed"),
+    ])
+
+    cert = (
+        x509.CertificateBuilder()
+        .subject_name(subject)
+        .issuer_name(issuer)
+        .public_key(key.public_key())
+        .serial_number(x509.random_serial_number())
+        .not_valid_before(datetime.now(timezone.utc))
+        .not_valid_after(datetime.now(timezone.utc) + timedelta(days=365))
+        .add_extension(
+            x509.SubjectAlternativeName([
+                x509.DNSName("localhost"),
+                x509.IPAddress(ipaddress.IPv4Address("127.0.0.1")),
+            ]),
+            critical=False,
+        )
+        .sign(key, hashes.SHA256())
+    )
+
+    key_path.write_bytes(
+        key.private_bytes(
+            encoding=serialization.Encoding.PEM,
+            format=serialization.PrivateFormat.TraditionalOpenSSL,
+            encryption_algorithm=serialization.NoEncryption(),
+        )
+    )
+    cert_path.write_bytes(cert.public_bytes(serialization.Encoding.PEM))
+
+    return cert_path, key_path
+
 
 def run_server(
     host: str = "0.0.0.0",
     port: int = 8000,
     password: Optional[str] = None,
-    workers: int = 1,
+    cert_path: Optional[str] = None,
+    key_path: Optional[str] = None,
+    no_tls: bool = False,
 ) -> None:
     app = create_app(password=password or "")
 
+    ssl_ctx = None
+    if not no_tls:
+        if cert_path and key_path:
+            c, k = Path(cert_path), Path(key_path)
+        else:
+            c, k = ensure_tls_certs()
+            print(f"[TLS] Auto-generated self-signed cert: {c}")
+
+        ssl_ctx = ssl.SSLContext(ssl.PROTOCOL_TLS_SERVER)
+        ssl_ctx.load_cert_chain(str(c), str(k))
+        protocol = "https"
+    else:
+        print("[WARNING] TLS disabled — all traffic is unencrypted!")
+        protocol = "http"
+
+    print(f"[ADMIN] Clear token: {app.ctx.admin_token}")
+    print(f"[SERVER] Listening on {protocol}://{host}:{port}")
+
     app.run(
         host=host,
         port=port,
         single_process=True,
         debug=False,
-        access_log=True,
+        access_log=False,
+        ssl=ssl_ctx,
     )