MCP OAuth tokens for HTTP servers not reliably reused across sessions — duplicate cache-key entries force repeated re-auth

Describe the bug

For an HTTP-type MCP server that uses OAuth (PKCE, public client — clientSecret: null), Copilot CLI appears to mint a new token-cache entry under a different cache-key hash more often than expected, instead of finding and reusing the one still-valid cached token for that server.

Over about 3 weeks of normal use, I have 13 separate <hash>.tokens.json files in ~/.copilot/mcp-oauth-config/ that are all for the exact same server URL + OAuth scope, when I'd expect at most one entry that gets updated/refreshed in place. Only 1 matching <hash>.json client-registration file exists for that server, so the token-cache key and the client-registration key appear to diverge over time.

Two of the 13 token files were written in the same second and contain byte-identical expiresAt epoch values, which strongly suggests a single OAuth completion got persisted under two different cache-key hashes rather than one canonical entry being reused.

Separately (possibly independent, possibly compounding): none of the 13 cached tokens contain a refreshToken field — only accessToken + expiresAt. Observed access-token lifetime is consistently ~75–90 minutes. Since there's no refresh token, once it expires there is no silent-refresh path and the full interactive browser consent flow must run again. Combined with the cache-key issue above, the net effect looks like "the token expires in under an hour and I constantly have to re-authenticate," when it's really a mix of (a) a genuinely short-lived, non-refreshable token, and (b) the client sometimes failing to locate a still-valid cached token for the same server.

Affected version

1.0.80

Steps to reproduce the behavior

1. Configure an HTTP MCP server that requires OAuth (registered in ~/.copilot/mcp-config.json with "type": "http", pointing at a server behind an internal API gateway).
2. Authenticate once via the interactive browser flow.
3. Use the tool across multiple CLI sessions (including separate worktree-backed sessions) over several days.
4. Inspect ~/.copilot/mcp-oauth-config/*.tokens.json — instead of a single file per server updated in place, multiple files accumulate for the identical server URL/scope. Some have expiresAt values identical to the second with another file.
5. In practice this surfaces as being prompted to re-authenticate noticeably more often than the access token's actual ~75–90 minute lifetime would suggest, i.e. sessions don't always find/reuse an already-valid cached token.

Expected behavior

• A given MCP server's OAuth token cache entry should be looked up and updated using a single, stable cache key (e.g., derived only from server/resource URL + client ID), not one that can vary across otherwise-identical auth attempts for the same server.
• When a still-valid, non-expired cached token already exists for a server, any session should find and reuse it rather than triggering a fresh interactive login.
• If a variable value (such as the randomly chosen local loopback redirect port used during the OAuth flow) is unintentionally being folded into the persisted cache-key, that would explain the duplicate-key behavior observed above.

Additional context

• OS: Windows 11 (Windows_NT)
• MCP server type: http, OAuth with PKCE, public client
• Token cache directory (~/.copilot/mcp-oauth-config/) is per-user/global, not per-session, so in principle tokens should already be shareable across sessions/worktrees on the same machine — but the duplicate cache-key entries above show that reuse isn't happening reliably.
• Observed access-token lifetimes across 13 samples for the same server: consistently ~75–90 minutes.
• No refreshToken field present in any of the 13 cached token files for this server.
• Docs describe mcp-oauth-config/ as file-based storage used "when keychain-backed storage is unavailable." On this machine (Windows 11 with Credential Manager available) it may be worth confirming why the file-based fallback path is being used at all, since that could be related to the cache-key inconsistency.

まず、レポートで指定されている OAuth 設定とキャッシュパスを調べます: ~/.copilot/mcp-config.json と ~/.copilot/mcp-oauth-config/*.tokens.json。HTTP MCP サーバーの URL、scope、client、loopback リダイレクトポートが永続化されるキャッシュキーにどのように寄与するかを追跡し、その後、別々の CLI セッション間で、有効な token エントリが重複したり対話的なログインを開始したりすることなく再利用されることを確認します。