Full OAuth Server

Build a self-contained authentication system where your FastMCP server manages users, issues tokens, and validates them.

Warning: This is an extremely advanced pattern that most users should avoid. Building a secure OAuth 2.1 server requires deep expertise in authentication protocols, cryptography, and security best practices. The complexity extends far beyond initial implementation to include ongoing security monitoring, threat response, and compliance maintenance.

Use Remote OAuth instead unless you have compelling requirements that external identity providers cannot meet, such as air-gapped environments or specialized compliance needs.

The Full OAuth Server pattern exists to support the MCP protocol specification's requirements. Your FastMCP server becomes both an Authorization Server and Resource Server, handling the complete authentication lifecycle from user login to token validation.

This documentation exists for completeness - the vast majority of applications should use external identity providers instead.

OAuthProvider

FastMCP provides the OAuthProvider abstract class that implements the OAuth 2.1 specification. To use this pattern, you must subclass OAuthProvider and implement all required abstract methods.

Note: OAuthProvider handles OAuth endpoints, protocol flows, and security requirements, but delegates all storage, user management, and business logic to your implementation of the abstract methods.

Required Implementation

You must implement these abstract methods to create a functioning OAuth server:

Client Management

Retrieve client information by ID from your database.


  
    Client identifier to look up
  



  
    Client information object or `None` if client not found
  




Store new client registration information in your database.


  
    Complete client registration information to store
  



  
    No return value

Authorization Flow

Handle authorization request and return redirect URL. Must implement user authentication and consent collection.


  
    OAuth client making the authorization request
  

  
    Authorization request parameters from the client
  



  
    Redirect URL to send the client to
  




Load authorization code from storage by code string. Return `None` if code is invalid or expired.


  
    OAuth client attempting to use the authorization code
  

  
    Authorization code string to look up
  



  
    Authorization code object or `None` if not found

Token Management

Exchange authorization code for access and refresh tokens. Must validate code and create new tokens.


  
    OAuth client exchanging the authorization code
  

  
    Valid authorization code object to exchange
  



  
    New OAuth token containing access and refresh tokens
  




Load refresh token from storage by token string. Return `None` if token is invalid or expired.


  
    OAuth client attempting to use the refresh token
  

  
    Refresh token string to look up
  



  
    Refresh token object or `None` if not found
  




Exchange refresh token for new access/refresh token pair. Must validate scopes and token.


  
    OAuth client using the refresh token
  

  
    Valid refresh token object to exchange
  

  
    Requested scopes for the new access token
  



  
    New OAuth token with updated access and refresh tokens
  




Load an access token by its token string.


  
    The access token to verify
  



  
    The access token object, or `None` if the token is invalid
  




Revoke access or refresh token, marking it as invalid in storage.


  
    Token object to revoke and mark invalid
  



  
    No return value
  




Verify bearer token for incoming requests. Return `AccessToken` if valid, `None` if invalid.


  
    Bearer token string from incoming request
  



  
    Access token object if valid, `None` if invalid or expired

Each method must handle storage, validation, security, and error cases according to the OAuth 2.1 specification. The implementation complexity is substantial and requires expertise in OAuth security considerations.

Warning: Security Notice: OAuth server implementation involves numerous security considerations including PKCE, state parameters, redirect URI validation, token binding, replay attack prevention, and secure storage requirements. Mistakes can lead to serious security vulnerabilities.

Documentation Index

Fetch the complete documentation index at: https://gofastmcp.com/llms.txt Use this file to discover all available pages before exploring further.

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