fix: restore OAuth token expiry across process restarts

src/mcp/client/auth/extensions/client_credentials.py

@@ -78,6 +78,7 @@ async def _initialize(self) -> None:
         """Load stored tokens and set pre-configured client_info."""
         self.context.current_tokens = await self.context.storage.get_tokens()
         self.context.client_info = self._fixed_client_info
+        self.context.restore_token_expiry()
         self._initialized = True
 
     async def _perform_authorization(self) -> httpx2.Request:
@@ -292,6 +293,7 @@ async def _initialize(self) -> None:
         """Load stored tokens and set pre-configured client_info."""
         self.context.current_tokens = await self.context.storage.get_tokens()
         self.context.client_info = self._fixed_client_info
+        self.context.restore_token_expiry()
         self._initialized = True
 
     async def _perform_authorization(self) -> httpx2.Request:

src/mcp/client/auth/oauth2.py

@@ -180,6 +180,19 @@ def update_token_expiry(self, token: OAuthToken) -> None:
         """Update token expiry time using shared util function."""
         self.token_expiry_time = calculate_token_expiry(token.expires_in)
 
+    def restore_token_expiry(self) -> None:
+        """Restore ``token_expiry_time`` from the persisted absolute expiry.
+
+        ``_initialize`` reloads ``current_tokens`` from storage, but the stored
+        ``OAuthToken`` only carries the relative ``expires_in``, so the absolute
+        expiry must be persisted separately (``expires_at``) and restored here.
+        Without it, ``is_token_valid()`` treats an already-expired access token
+        as valid on a fresh process and sends a stale Bearer, wasting a 401
+        round-trip before re-authentication.
+        """
+        if self.current_tokens and self.current_tokens.expires_at is not None:
+            self.token_expiry_time = self.current_tokens.expires_at
+
     def is_token_valid(self) -> bool:
         """Check if current token is valid."""
         return bool(
@@ -484,6 +497,8 @@ async def _handle_token_response(self, response: httpx2.Response) -> None:
         # Store tokens in context
         self.context.current_tokens = token_response
         self.context.update_token_expiry(token_response)
+        # Persist the absolute expiry so it survives a process restart
+        token_response.expires_at = self.context.token_expiry_time
         await self.context.storage.set_tokens(token_response)
 
     async def _refresh_token(self) -> httpx2.Request:
@@ -539,6 +554,7 @@ async def _handle_refresh_response(self, response: httpx2.Response) -> bool:
 
             self.context.current_tokens = token_response
             self.context.update_token_expiry(token_response)
+            token_response.expires_at = self.context.token_expiry_time
             await self.context.storage.set_tokens(token_response)
 
             return True
@@ -551,6 +567,7 @@ async def _initialize(self) -> None:
         """Load stored tokens and client info."""
         self.context.current_tokens = await self.context.storage.get_tokens()
         self.context.client_info = await self.context.storage.get_client_info()
+        self.context.restore_token_expiry()
         self._initialized = True
 
     def _add_auth_header(self, request: httpx2.Request) -> None:

src/mcp/shared/auth.py

@@ -29,6 +29,7 @@ class OAuthToken(BaseModel):
     access_token: str
     token_type: Literal["Bearer"] = "Bearer"
     expires_in: int | None = None
+    expires_at: float | None = None
     scope: str | None = None
     refresh_token: str | None = None
 

tests/client/auth/extensions/test_client_credentials.py

@@ -1,3 +1,4 @@
+import time
 import urllib.parse
 
 import jwt
@@ -94,6 +95,30 @@ async def test_init_with_client_secret_post(self, mock_storage: MockTokenStorage
         assert provider.context.client_info is not None
         assert provider.context.client_info.token_endpoint_auth_method == "client_secret_post"
 
+    @pytest.mark.anyio
+    async def test_init_restores_expired_token_expiry(self, mock_storage: MockTokenStorage):
+        """_initialize must restore token_expiry_time from the persisted expires_at.
+
+        Regression for the stale-Bearer bug: without restoring the absolute
+        expiry, an already-expired access token looks valid after a restart and
+        a 401 round-trip is wasted before re-auth.
+        """
+        mock_storage._tokens = OAuthToken(
+            access_token="expired-token",
+            expires_at=time.time() - 10,  # already expired
+        )
+        provider = ClientCredentialsOAuthProvider(
+            server_url="https://api.example.com",
+            storage=mock_storage,
+            client_id="test-client-id",
+            client_secret="test-client-secret",
+        )
+
+        await provider._initialize()
+
+        assert provider.context.token_expiry_time is not None
+        assert not provider.context.is_token_valid()
+
     @pytest.mark.anyio
     async def test_exchange_token_client_credentials(self, mock_storage: MockTokenStorage):
         """Test token exchange request building."""