fastmcp.client.auth.client_credentials

Machine-to-machine (M2M) OAuth client authentication for FastMCP.

These providers authenticate a FastMCP client to a protected MCP server without a browser, using the OAuth 2.0 client_credentials grant:

• ClientCredentialsOAuthProvider authenticates with a client_id and client_secret (the common M2M case).
• PrivateKeyJWTOAuthProvider authenticates with an RFC 7523 private_key_jwt client assertion (workload identity federation, or a locally signed JWT).

Both are thin wrappers over the MCP SDK's client-credentials providers. Like the interactive OAuth provider, they can be constructed without an mcp_url and bound to the server URL automatically when passed to Client(auth=...).

Classes

ClientCredentialsOAuthProvider ^{<a href="https://github.com/PrefectHQ/fastmcp/blob/main/fastmcp_slim/fastmcp/client/auth/client_credentials.py#L164" target="_blank"><Icon icon="github" style="width: 14px; height: 14px;" /></a>}

OAuth client_credentials provider using a client ID and secret.

This is the standard machine-to-machine flow: the client exchanges its client_id and client_secret at the authorization server's token endpoint for an access token, which is then attached to every request. The token endpoint is discovered from the MCP server's OAuth metadata, so callers provide the MCP server URL rather than a raw token endpoint.

Methods:

async_auth_flow ^{<a href="https://github.com/PrefectHQ/fastmcp/blob/main/fastmcp_slim/fastmcp/client/auth/client_credentials.py#L258" target="_blank"><Icon icon="github" style="width: 14px; height: 14px;" /></a>}

async_auth_flow(self, request: httpx2.Request) -> AsyncGenerator[httpx2.Request, httpx2.Response]

PrivateKeyJWTOAuthProvider ^{<a href="https://github.com/PrefectHQ/fastmcp/blob/main/fastmcp_slim/fastmcp/client/auth/client_credentials.py#L281" target="_blank"><Icon icon="github" style="width: 14px; height: 14px;" /></a>}

OAuth client_credentials provider using private_key_jwt (RFC 7523).

Instead of a shared client secret, the client authenticates to the token endpoint with a signed JWT assertion. The assertion_provider callback receives the authorization server's issuer identifier (the required JWT audience) and returns the assertion. Use SignedJWTParameters.create_assertion_provider() to sign locally with a private key, static_assertion_provider() for a pre-built JWT, or supply your own callback for workload identity federation.

Methods:

async_auth_flow ^{<a href="https://github.com/PrefectHQ/fastmcp/blob/main/fastmcp_slim/fastmcp/client/auth/client_credentials.py#L384" target="_blank"><Icon icon="github" style="width: 14px; height: 14px;" /></a>}

async_auth_flow(self, request: httpx2.Request) -> AsyncGenerator[httpx2.Request, httpx2.Response]