MCP OAuth

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MCP OAuth

LiteLLM supports two OAuth 2.0 flows for MCP servers:

Interactive OAuth (PKCE)

For user-facing MCP clients (Claude Code, Cursor), LiteLLM supports the full OAuth 2.0 authorization code flow with PKCE.

Setup

mcp_servers:
  github_mcp:
    url: "https://api.githubcopilot.com/mcp"
    auth_type: oauth2
    client_id: os.environ/GITHUB_OAUTH_CLIENT_ID
    client_secret: os.environ/GITHUB_OAUTH_CLIENT_SECRET

See Claude Code Tutorial

How It Works

sequenceDiagram
    participant Browser as User-Agent (Browser)
    participant Client as Client
    participant LiteLLM as LiteLLM Proxy
    participant MCP as MCP Server (Resource Server)
    participant Auth as Authorization Server

    Note over Client,LiteLLM: Step 1 – Resource discovery
    Client->>LiteLLM: GET /.well-known/oauth-protected-resource/{mcp_server_name}/mcp
    LiteLLM->>Client: Return resource metadata

    Note over Client,LiteLLM: Step 2 – Authorization server discovery
    Client->>LiteLLM: GET /.well-known/oauth-authorization-server/{mcp_server_name}
    LiteLLM->>Client: Return authorization server metadata

    Note over Client,Auth: Step 3 – Dynamic client registration
    Client->>LiteLLM: POST /{mcp_server_name}/register
    LiteLLM->>Auth: Forward registration request
    Auth->>LiteLLM: Issue client credentials
    LiteLLM->>Client: Return client credentials

    Note over Client,Browser: Step 4 – User authorization (PKCE)
    Client->>Browser: Open authorization URL + code_challenge + resource
    Browser->>Auth: Authorization request
    Note over Auth: User authorizes
    Auth->>Browser: Redirect with authorization code
    Browser->>LiteLLM: Callback to LiteLLM with code
    LiteLLM->>Browser: Redirect back with authorization code
    Browser->>Client: Callback with authorization code

    Note over Client,Auth: Step 5 – Token exchange
    Client->>LiteLLM: Token request + code_verifier + resource
    LiteLLM->>Auth: Forward token request
    Auth->>LiteLLM: Access (and refresh) token
    LiteLLM->>Client: Return tokens

    Note over Client,MCP: Step 6 – Authenticated MCP call
    Client->>LiteLLM: MCP request with access token + LiteLLM API key
    LiteLLM->>MCP: MCP request with Bearer token
    MCP-->>LiteLLM: MCP response
    LiteLLM-->>Client: Return MCP response

Participants

• Client -- The MCP-capable AI agent (e.g., Claude Code, Cursor, or another IDE/agent) that initiates OAuth discovery, authorization, and tool invocations on behalf of the user.
• LiteLLM Proxy -- Mediates all OAuth discovery, registration, token exchange, and MCP traffic while protecting stored credentials.
• Authorization Server -- Issues OAuth 2.0 tokens via dynamic client registration, PKCE authorization, and token endpoints.
• MCP Server (Resource Server) -- The protected MCP endpoint that receives LiteLLM's authenticated JSON-RPC requests.
• User-Agent (Browser) -- Temporarily involved so the end user can grant consent during the authorization step.

Flow Steps

1. Resource Discovery: The client fetches MCP resource metadata from LiteLLM's .well-known/oauth-protected-resource endpoint to understand scopes and capabilities.
2. Authorization Server Discovery: The client retrieves the OAuth server metadata (token endpoint, authorization endpoint, supported PKCE methods) through LiteLLM's .well-known/oauth-authorization-server endpoint.
3. Dynamic Client Registration: The client registers through LiteLLM, which forwards the request to the authorization server (RFC 7591). If the provider doesn't support dynamic registration, you can pre-store client_id/client_secret in LiteLLM (e.g., GitHub MCP) and the flow proceeds the same way.
4. User Authorization: The client launches a browser session (with code challenge and resource hints). The user approves access, the authorization server sends the code through LiteLLM back to the client.
5. Token Exchange: The client calls LiteLLM with the authorization code, code verifier, and resource. LiteLLM exchanges them with the authorization server and returns the issued access/refresh tokens.
6. MCP Invocation: With a valid token, the client sends the MCP JSON-RPC request (plus LiteLLM API key) to LiteLLM, which forwards it to the MCP server and relays the tool response.

See the official MCP Authorization Flow for additional reference.

Machine-to-Machine (M2M) Auth

LiteLLM automatically fetches, caches, and refreshes OAuth2 tokens using the client_credentials grant. No manual token management required.

Setup

mcp_servers:
  my_mcp_server:
    url: "https://my-mcp-server.com/mcp"
    auth_type: oauth2
    client_id: os.environ/MCP_CLIENT_ID
    client_secret: os.environ/MCP_CLIENT_SECRET
    token_url: "https://auth.example.com/oauth/token"
    scopes: ["mcp:read", "mcp:write"]  # optional

Navigate to MCP Servers → Add Server → Authentication → OAuth, then fill in client_id, client_secret, and token_url.

How It Works

1. On first MCP request, LiteLLM POSTs to token_url with grant_type=client_credentials
2. The access token is cached in-memory with TTL = expires_in - 60s
3. Subsequent requests reuse the cached token
4. When the token expires, LiteLLM fetches a new one automatically

sequenceDiagram
    participant Client as Client
    participant LiteLLM as LiteLLM Proxy
    participant Auth as Authorization Server
    participant MCP as MCP Server

    Client->>LiteLLM: MCP request + LiteLLM API key
    LiteLLM->>Auth: POST /oauth/token (client_credentials)
    Auth->>LiteLLM: access_token (expires_in: 3600)
    LiteLLM->>MCP: MCP request + Bearer token
    MCP-->>LiteLLM: MCP response
    LiteLLM-->>Client: MCP response

    Note over LiteLLM: Token cached for subsequent requests
    Client->>LiteLLM: Next MCP request
    LiteLLM->>MCP: MCP request + cached Bearer token
    MCP-->>LiteLLM: MCP response
    LiteLLM-->>Client: MCP response

Test with Mock Server

Use BerriAI/mock-oauth2-mcp-server to test locally:

pip install fastapi uvicorn
python mock_oauth2_mcp_server.py  # starts on :8765

mcp_servers:
  test_oauth2:
    url: "http://localhost:8765/mcp"
    auth_type: oauth2
    client_id: "test-client"
    client_secret: "test-secret"
    token_url: "http://localhost:8765/oauth/token"

litellm --config config.yaml --port 4000

# List tools
curl http://localhost:4000/mcp-rest/tools/list \
  -H "Authorization: Bearer sk-1234"

# Call a tool
curl http://localhost:4000/mcp-rest/tools/call \
  -H "Content-Type: application/json" \
  -H "Authorization: Bearer sk-1234" \
  -d '{"name": "echo", "arguments": {"message": "hello"}}'

Config Reference