Remote MCP (OAuth): expired access token forces interactive re-auth instead of silent refresh_token grant #4203

Summary

When a remote OAuth-protected MCP server's cached access token is expired at session start, the Copilot CLI treats the server as needing a fresh interactive OAuth login and drops its tools — even though a valid refresh token is cached. It never attempts an RFC 6749 §6 refresh_token grant. In non-interactive/automation sessions the interactive flow can't complete, so the server's tools silently never load.

Environment

• GitHub Copilot CLI 1.0.71, running inside VS Code
• macOS (Darwin); credential store = Apple Keychain (copilot-mcp-oauth)
• MCP transport: rmcp streamable HTTP (rmcp::transport::worker / ::streamable), reqwest 0.13.4

Configuration

• Remote HTTP MCP server in ~/.copilot/mcp-config.json:

  "notion": { "type": "http", "url": "https://mcp.notion.com/mcp" }

• Cached grant in Keychain (service copilot-mcp-oauth, account <hash>) and ~/.copilot/mcp-oauth-config/<hash>.tokens.json — contains accessToken, expiresAt, refreshToken.
• Server authorization-server metadata (RFC 8414) advertises refresh support:
  token_endpoint: https://mcp.notion.com/token, grant_types_supported: ["authorization_code", "refresh_token"]

Steps to reproduce

1. Authenticate a remote OAuth MCP server (e.g. Notion) so a valid access+refresh grant is cached.
2. Let the access token expire while the refresh token stays valid (Notion access tokens last ~8h — e.g. leave it overnight).
3. Start a new Copilot CLI session (especially a non-interactive/scheduled one).
4. Observe: the server's tools are absent from the session.

Observed behavior

From ~/.copilot/logs/process-<...>.log (redacted):

[ERROR] Starting remote MCP client for notion with url: https://mcp.notion.com/mcp
[ERROR] Connecting MCP client for notion...
        -> connects to mcp.notion.com:443 using the cached (expired) access token
[ERROR] [rust:rmcp::transport::worker] worker quit with fatal: Transport channel closed,
        when Client(OAuthChallenge { www_authenticate_header:
        "...OAuth, resource_metadata=\".../.well-known/oauth-protected-resource/mcp\",
        error=\"invalid_token\", error_description=\"Mis...\"" })
[ERROR] Server notion requires authentication, initiating OAuth flow
[ERROR] OAuth authentication required for notion

The runtime then reads the cached OAuth entry from Keychain but still ends at "OAuth authentication required."

Evidence that no refresh was attempted

Grep of the entire session-start process log:

POSTs to mcp.notion.com/token : 0

Zero refresh_token grants were sent, despite a valid refresh token being cached.

Expected behavior

On a 401 / WWW-Authenticate: … error="invalid_token" for a server that has a cached refresh token:

1. Silently POST grant_type=refresh_token (+ client_id) to the discovered token_endpoint.
2. Persist the rotated access/refresh tokens.
3. Reconnect and load the server's tools.
4. Only fall back to the interactive OAuth flow if the refresh itself fails (invalid_grant, expired/revoked).

Impact

• Any remote OAuth MCP server silently loses its tools once the access token expires, until a manual re-auth — even though the refresh token is valid and the whole point of storing it is to avoid exactly this.
• Breaks unattended/scheduled sessions (e.g. a daily automation), where the interactive prompt can never be completed.

Likely root cause / where to look

• The rmcp streamable transport surfaces the OAuth challenge as a fatal transport error ("worker quit with fatal … OAuthChallenge"), and the CLI's handler maps "auth required" directly to the interactive flow without first attempting a token refresh.
• Secondary: the session's tool list appears to be snapshotted at startup, so even a later successful (re)auth doesn't surface the tools into an already-running session.

Suggested fix

• Insert a refresh step in the auth-challenge path: if a refresh_token is cached for the server, perform the refresh grant against the discovered token_endpoint, persist rotated tokens, and reconnect before considering interactive auth.
• Optionally refresh proactively when expiresAt is at/near expiry before the first connect.
• Consider re-syncing tools into active sessions after a late auth success.

Workaround

• Manually perform the refresh_token grant against the token_endpoint, write the rotated tokens back into the cache; or re-run the CLI's interactive auth for the server before starting the session.

cc @connor4312 (VS Code team)

_{Filed with assistance from GitHub Copilot CLI.}