feat: implement concrete OAuth provider with in-memory storage

OAuthProvider is abstract — subclassed as HomelabOAuth with full
implementation of register_client, get_client, create/exchange
authorization codes, token issuance, PKCE verification, and
refresh token rotation.

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

mcp_bridge/mcp_server.py

@@ -5,8 +5,13 @@ import logging
 from datetime import datetime, timezone
 
 from fastmcp import FastMCP
-from fastmcp.server.auth import OAuthProvider
+import secrets
+import time
+import hashlib
+
+from fastmcp.server.auth import OAuthProvider, AccessToken
 from fastmcp.server.auth.auth import ClientRegistrationOptions
+from mcp.shared.auth import OAuthClientInformationFull, OAuthToken
 from starlette.requests import Request
 from starlette.responses import JSONResponse
 from starlette.routing import Route
@@ -19,8 +24,136 @@ logger = logging.getLogger(__name__)
 # Will be initialized in __main__ with shared db instance
 db: Database | None = None
 
-# OAuth provider with Dynamic Client Registration enabled
-oauth = OAuthProvider(
+TOKEN_LIFETIME = 3600
+
+
+class HomelabOAuth(OAuthProvider):
+    """Concrete OAuth provider with in-memory storage."""
+
+    def __init__(self, **kwargs):
+        super().__init__(**kwargs)
+        self._clients: dict[str, OAuthClientInformationFull] = {}
+        self._auth_codes: dict[str, dict] = {}  # code -> {client_id, code_challenge, redirect_uri, expires}
+        self._tokens: dict[str, dict] = {}  # token_hash -> {client_id, scopes, expires}
+        self._refresh_tokens: dict[str, dict] = {}  # refresh_hash -> {client_id, scopes}
+
+    async def register_client(self, client_info: OAuthClientInformationFull) -> None:
+        self._clients[client_info.client_id] = client_info
+        logger.info(f"Registered OAuth client: {client_info.client_id} ({client_info.client_name})")
+
+    async def get_client(self, client_id: str) -> OAuthClientInformationFull | None:
+        return self._clients.get(client_id)
+
+    async def create_authorization_code(
+        self, client: OAuthClientInformationFull, code_challenge: str | None,
+        redirect_uri: str | None, scopes: list[str] | None = None,
+        **kwargs,
+    ) -> str:
+        code = secrets.token_urlsafe(32)
+        self._auth_codes[code] = {
+            "client_id": client.client_id,
+            "code_challenge": code_challenge,
+            "redirect_uri": redirect_uri or str(client.redirect_uris[0]),
+            "scopes": scopes or [],
+            "expires": time.time() + 300,
+        }
+        logger.info(f"Auth code issued for client {client.client_id}")
+        return code
+
+    async def exchange_authorization_code(
+        self, client: OAuthClientInformationFull, code: str,
+        code_verifier: str | None = None, redirect_uri: str | None = None,
+        **kwargs,
+    ) -> OAuthToken:
+        if code not in self._auth_codes:
+            raise ValueError("Invalid authorization code")
+
+        code_data = self._auth_codes.pop(code)
+
+        if code_data["expires"] < time.time():
+            raise ValueError("Authorization code expired")
+
+        if code_data["client_id"] != client.client_id:
+            raise ValueError("Client ID mismatch")
+
+        # PKCE verification
+        if code_data["code_challenge"] and code_verifier:
+            import base64
+            digest = hashlib.sha256(code_verifier.encode("ascii")).digest()
+            computed = base64.urlsafe_b64encode(digest).rstrip(b"=").decode("ascii")
+            if computed != code_data["code_challenge"]:
+                raise ValueError("PKCE verification failed")
+
+        # Issue tokens
+        access_token = secrets.token_urlsafe(48)
+        refresh_token = secrets.token_urlsafe(48)
+
+        self._tokens[hashlib.sha256(access_token.encode()).hexdigest()] = {
+            "client_id": client.client_id,
+            "scopes": code_data["scopes"],
+            "expires": time.time() + TOKEN_LIFETIME,
+        }
+        self._refresh_tokens[hashlib.sha256(refresh_token.encode()).hexdigest()] = {
+            "client_id": client.client_id,
+            "scopes": code_data["scopes"],
+        }
+
+        logger.info(f"Token issued for client {client.client_id}")
+        return OAuthToken(
+            access_token=access_token,
+            token_type="Bearer",
+            expires_in=TOKEN_LIFETIME,
+            refresh_token=refresh_token,
+            scope=" ".join(code_data["scopes"]) if code_data["scopes"] else None,
+        )
+
+    async def load_access_token(self, token: str) -> AccessToken | None:
+        token_hash = hashlib.sha256(token.encode()).hexdigest()
+        data = self._tokens.get(token_hash)
+        if not data or data["expires"] < time.time():
+            return None
+        return AccessToken(
+            token=token,
+            client_id=data["client_id"],
+            scopes=data["scopes"],
+        )
+
+    async def exchange_refresh_token(
+        self, client: OAuthClientInformationFull,
+        refresh_token: str, scopes: list[str] | None = None,
+        **kwargs,
+    ) -> OAuthToken:
+        refresh_hash = hashlib.sha256(refresh_token.encode()).hexdigest()
+        data = self._refresh_tokens.get(refresh_hash)
+        if not data or data["client_id"] != client.client_id:
+            raise ValueError("Invalid refresh token")
+
+        # Issue new tokens
+        new_access = secrets.token_urlsafe(48)
+        new_refresh = secrets.token_urlsafe(48)
+
+        self._tokens[hashlib.sha256(new_access.encode()).hexdigest()] = {
+            "client_id": client.client_id,
+            "scopes": scopes or data["scopes"],
+            "expires": time.time() + TOKEN_LIFETIME,
+        }
+        # Rotate refresh token
+        del self._refresh_tokens[refresh_hash]
+        self._refresh_tokens[hashlib.sha256(new_refresh.encode()).hexdigest()] = {
+            "client_id": client.client_id,
+            "scopes": scopes or data["scopes"],
+        }
+
+        return OAuthToken(
+            access_token=new_access,
+            token_type="Bearer",
+            expires_in=TOKEN_LIFETIME,
+            refresh_token=new_refresh,
+            scope=" ".join(scopes or data["scopes"]) if (scopes or data["scopes"]) else None,
+        )
+
+
+oauth = HomelabOAuth(
     base_url="https://mcp.georgsen.dk",
     client_registration_options=ClientRegistrationOptions(enabled=True),
 )