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

# middleware

# `fastmcp.server.auth.middleware`

Enhanced authentication middleware with better error messages.

This module provides enhanced versions of MCP SDK authentication middleware
that return more helpful error messages for developers troubleshooting
authentication issues.

Implements RFC 6750 §3.1 compliance by distinguishing between missing
authentication (no error attribute) and invalid authentication (with error).

## Classes

### `RequireAuthMiddleware` <sup>[https://github.com/PrefectHQ/fastmcp/blob/main/fastmcp\_slim/fastmcp/server/auth/middleware.py#L27](https://github.com/PrefectHQ/fastmcp/blob/main/fastmcp_slim/fastmcp/server/auth/middleware.py#L27)</sup>

Enhanced authentication middleware with detailed error messages.

Extends the SDK's RequireAuthMiddleware to provide more actionable
error messages when authentication fails. This helps developers
understand what went wrong and how to fix it.

Also implements RFC 6750 §3.1 compliance by distinguishing between
missing authentication (initial discovery) and invalid authentication
(token validation failure).


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