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MCP pinned provider credentials (custom servers)

Overview​

Custom MCP servers created in the UI can pin a specific provider connection (OAuth) so every authorized caller uses that connection's token — not their own connected app.

Built-in MCP servers (github, jira, gitlab, etc. from config.yaml) keep the existing per-caller provider resolution with optional fallback_env.

Motivation​

Operators configure an MCP server with a service-user's Atlassian/GitHub connection and expect all chat users to act through that identity. Today provider on the credential source overrides provider_connection_id at runtime, so the invoking user's OAuth wins instead.

Design​

Schema: connection_scope on MCPCredentialSource​

ValueMeaning
caller (default)Resolve provider for JWT sub; optional fallback_env
pinnedAlways provider_connection_id; fail if missing/invalid

Pinned sources store provider_connection_id + connection_scope: "pinned". Do not persist provider for resolution (built-ins keep provider only).

Resolution (BFF + Dynamic Agents — identical order)​

  1. connection_scope === "pinned" → exchange provider_connection_id; no fallback_env
  2. Else if provider → per-caller exchange by provider key
  3. Else if provider_connection_id → legacy ID exchange
  4. Else caller path fallbacks (fallback_env, fallback_client_credentials)

Pinned failure → MCP_CREDENTIAL_UNAVAILABLE (HTTP 401 on test/probe paths).

Authorization for pinned exchange​

Non-owners may refresh a pinned connection when:

  • mcp_server:<id>#can_use and the server's credential_sources pins that provider_connection_id (POST /api/credentials/exchange accepts optional mcp_server_id for this path), or
  • secret_ref:provider_connection:<id>#can_use (existing share model)

UI (custom servers only)​

MCP Server Editor shows Connection scope when kind = Connected app and the server is not config-driven:

  • Use this connection for all callers (pinned) — default for new credentials
  • Use each caller's connection (caller)

Out of scope​

  • Built-in / config-driven MCP servers (config.yaml)
  • Changing GitHub/GitLab hybrid PAT fallback behavior

Acceptance criteria​

  • Custom server with connection_scope: pinned persists without provider
  • Test modal and Dynamic Agents use pinned connection ID for any authorized caller
  • Missing/disconnected pinned connection returns 401 (no silent skip, no PAT fallback)
  • connection_scope: caller + provider unchanged for per-user OAuth
  • Built-in github/jira seeds unchanged
  • E2E: create pinned server, second user test uses pinned ID; invalid pinned → error