FastAPI + FastMCP OAuth Authentication with Scalekit

Overview

This skill documents the pattern for building production-ready MCP (Model Context Protocol) servers using FastAPI and FastMCP with OAuth 2.1 Bearer token authentication via Scalekit. This approach provides fine-grained control over authentication middleware, token validation, and server behavior compared to using FastMCP's built-in OAuth provider.

When to Use This Pattern

Use this FastAPI + FastMCP integration when you need:

• Custom middleware requirements: Implement rate limiting, request logging, or complex authorization logic beyond basic token validation
• Existing FastAPI applications: Integrate MCP tools into established FastAPI codebases without rewriting
• Advanced authorization: Enforce scope-based access control, multi-tenancy, or custom claims validation
• Full HTTP control: Manage CORS policies, health checks, and multiple endpoints alongside MCP tools
• Production requirements: Add monitoring, metrics, and deployment-specific configurations

Don't use this pattern if FastMCP's built-in OAuth provider meets your needs—the additional FastAPI layer adds complexity.

Core Architecture