OAuth Client Credentials

Machine-to-machine authentication for MCP using the OAuth 2.0 client credentials flow

The OAuth Client Credentials extension (io.modelcontextprotocol/oauth-client-credentials) adds support for the OAuth 2.0 client credentials flow to MCP. This enables automated systems to connect to MCP servers without interactive user authorization.

Specification

Full technical specification for the OAuth Client Credentials extension.

What it is

The standard MCP authorization flow requires a user to interactively approve access — a browser opens, the user logs in, and grants permission. That works well for humans, but breaks down when there’s no user present.

The OAuth Client Credentials extension solves this by letting a client authenticate using application-level credentials (a client ID and secret, or a signed JWT assertion) rather than delegated user credentials. The client proves its identity directly to the authorization server, which issues an access token without requiring a browser redirect or user interaction.

When to use it

Use OAuth Client Credentials when:

• Background services need to call MCP tools on a schedule or in response to events, without a user present
• CI/CD pipelines invoke MCP servers as part of automated build, test, or deployment workflows
• Server-to-server integrations connect two backend systems where there’s no end user involved
• Daemon processes or long-running workers need persistent access to MCP resources

If your integration has a human user who should explicitly authorize access, use the standard MCP authorization flow instead.

How it works

The extension supports two credential formats:

JWT Bearer Assertions (recommended)

Defined in RFC 7523, JWT Bearer Assertions let the client sign a token with its private key and present it as proof of identity. The authorization server validates the signature using the client’s registered public key.

The JWT assertion typically includes:

• iss: Client ID (the issuer)
• sub: Client ID (subject being authenticated)
• aud: Authorization server token endpoint URL
• exp: Expiration time
• iat: Issued-at time

Client Secrets

For simpler deployments, the extension also supports the standard client credentials flow using a client_id and client_secret. The client sends its credentials directly to the authorization server’s token endpoint and receives an access token in return.

Client secrets are long-lived credentials that grant access without user interaction. If a secret is leaked, an attacker can silently authenticate as your application until the secret is rotated. To reduce risk:

• Store secrets in a secrets manager, never in source code or environment files checked into version control.
• Rotate secrets on a regular schedule and immediately after any suspected compromise.
• Scope credentials to the minimum permissions required.
• Prefer JWT assertions when possible — they are short-lived and do not require transmitting the signing key.

Implementation guide

For MCP clients

To use the OAuth Client Credentials extension, your client must:

1. Declare support

   Include the extension in the initialize request capabilities:

   {
     "capabilities": {
       "extensions": {
         "io.modelcontextprotocol/oauth-client-credentials": {}
       }
     }
   }
   
2. Obtain an access token

   Request a token from the authorization server using the client credentials grant before connecting to the MCP server.

3. Include the token

   Pass the token in the Authorization header of HTTP requests to the MCP server:

   Authorization: Bearer <access_token>
   
4. Handle token refresh

   Client credentials tokens typically have shorter lifetimes than user-delegated tokens. Implement token refresh logic to obtain a new token before expiry.

For MCP servers

To accept client credentials tokens, your server must:

1. Validate the token

   On each request, verify the JWT signature and claims against your authorization server’s public keys (usually via a JWKS endpoint).

2. Check scopes

   Ensure the token includes the required scopes for the requested operation.

3. Advertise support

   Optionally (but recommended for discoverability), include the extension in the initialize response:

   {
     "capabilities": {
       "extensions": {
         "io.modelcontextprotocol/oauth-client-credentials": {}
       }
     }
   }
   

SDK examples

The official MCP SDKs provide built-in support for client credentials authentication. Both handle token acquisition and refresh automatically.

1. Install the SDK

   TypeScript

   npm install @modelcontextprotocol/client
   

   Python

   pip install mcp
   
2. Create a provider and connect

   Choose the credential format that matches your setup:

   Using a client secret

   TypeScript

   import {
     Client,
     ClientCredentialsProvider,
     StreamableHTTPClientTransport,
   } from "@modelcontextprotocol/client";
   
   const provider = new ClientCredentialsProvider({
     clientId: "my-service",
     clientSecret: "s3cr3t",
   });
   
   const client = new Client(
     { name: "my-service", version: "1.0.0" },
     { capabilities: {} },
   );
   
   const transport = new StreamableHTTPClientTransport(
     new URL("https://mcp.example.com/mcp"),
     { authProvider: provider },
   );
   
   await client.connect(transport);
   
   // Use the client
   const tools = await client.listTools();
   console.log(
     "Available tools:",
     tools.tools.map((t) => t.name),
   );
   
   await transport.close();
   

   Python

   from mcp.client.auth.extensions.client_credentials import (
       ClientCredentialsOAuthProvider,
   )
   from mcp.client.streamable_http import streamablehttp_client
   from mcp import ClientSession
   
   provider = ClientCredentialsOAuthProvider(
       server_url="https://mcp.example.com/mcp",
       client_id="my-service",
       client_secret="s3cr3t",
       scopes="read write",
   )
   
   async with streamablehttp_client(
       "https://mcp.example.com/mcp",
       auth_provider=provider,
   ) as (read_stream, write_stream, _):
       async with ClientSession(read_stream, write_stream) as session:
           await session.initialize()
   
           # Use the client
           tools = await session.list_tools()
           print("Available tools:", [t.name for t in tools.tools])
   

   Using a JWT private key

   TypeScript

   import {
     Client,
     PrivateKeyJwtProvider,
     StreamableHTTPClientTransport,
   } from "@modelcontextprotocol/client";
   
   const provider = new PrivateKeyJwtProvider({
     clientId: "my-service",
     privateKey: process.env.CLIENT_PRIVATE_KEY_PEM,
     algorithm: "RS256",
   });
   
   const client = new Client(
     { name: "my-service", version: "1.0.0" },
     { capabilities: {} },
   );
   
   const transport = new StreamableHTTPClientTransport(
     new URL("https://mcp.example.com/mcp"),
     { authProvider: provider },
   );
   
   await client.connect(transport);
   
   // Use the client
   const tools = await client.listTools();
   console.log(
     "Available tools:",
     tools.tools.map((t) => t.name),
   );
   
   await transport.close();
   

   Python

   from mcp.client.auth.extensions.client_credentials import (
       PrivateKeyJWTOAuthProvider,
       SignedJWTParameters,
   )
   from mcp.client.streamable_http import streamablehttp_client
   from mcp import ClientSession
   
   # Create a signed JWT assertion provider from key parameters
   jwt_params = SignedJWTParameters(
       issuer="my-service",
       subject="my-service",
       signing_key=open("private_key.pem").read(),
       signing_algorithm="RS256",
       lifetime_seconds=300,
   )
   
   provider = PrivateKeyJWTOAuthProvider(
       server_url="https://mcp.example.com/mcp",
       client_id="my-service",
       assertion_provider=jwt_params.create_assertion_provider(),
       scopes="read write",
   )
   
   async with streamablehttp_client(
       "https://mcp.example.com/mcp",
       auth_provider=provider,
   ) as (read_stream, write_stream, _):
       async with ClientSession(read_stream, write_stream) as session:
           await session.initialize()
   
           # Use the client
           tools = await session.list_tools()
           print("Available tools:", [t.name for t in tools.tools])
   

Client support

Support for this extension varies by client. Extensions are opt-in and never active by default.

Check the client matrix for current implementation status across MCP clients.

Related resources

ext-auth repository

Source code and reference implementations

Full specification

Technical specification with normative requirements

RFC 6749 — Client Credentials Grant

The underlying OAuth 2.0 specification

RFC 7523 — JWT Bearer Assertions

JWT assertion format specification