authorization

fastmcp.server.middleware.authorization

Authorization middleware for FastMCP.

This module provides middleware-based authorization using callable auth checks. AuthMiddleware applies auth checks globally to all components on the server.

Example:

from fastmcp import FastMCP
from fastmcp.server.auth import require_auth, require_scopes, restrict_tag
from fastmcp.server.middleware import AuthMiddleware

# Require auth for all components
mcp = FastMCP(middleware=[
    AuthMiddleware(auth=require_auth)
])

# Tag-based: components tagged "admin" require "admin" scope
mcp = FastMCP(middleware=[
    AuthMiddleware(auth=restrict_tag("admin", scopes=["admin"]))
])

Classes

AuthMiddleware

Global authorization middleware using callable checks.

This middleware applies auth checks to all components (tools, resources, prompts) on the server. It uses the same callable API as component-level auth checks.

The middleware:

• Filters tools/resources/prompts from list responses based on auth checks
• Checks auth before tool execution, resource read, and prompt render
• Skips all auth checks for STDIO transport (no OAuth concept)

Args:

• auth: A single auth check function or list of check functions. All checks must pass for authorization to succeed (AND logic).

Methods:

on_list_tools

on_list_tools(self, context: MiddlewareContext[mt.ListToolsRequest], call_next: CallNext[mt.ListToolsRequest, Sequence[Tool]]) -> Sequence[Tool]

Filter tools/list response based on auth checks.

on_call_tool

on_call_tool(self, context: MiddlewareContext[mt.CallToolRequestParams], call_next: CallNext[mt.CallToolRequestParams, ToolResult]) -> ToolResult

Check auth before tool execution.

on_list_resources

on_list_resources(self, context: MiddlewareContext[mt.ListResourcesRequest], call_next: CallNext[mt.ListResourcesRequest, Sequence[Resource]]) -> Sequence[Resource]

Filter resources/list response based on auth checks.

on_read_resource

on_read_resource(self, context: MiddlewareContext[mt.ReadResourceRequestParams], call_next: CallNext[mt.ReadResourceRequestParams, ResourceResult]) -> ResourceResult

Check auth before resource read.

on_list_resource_templates

on_list_resource_templates(self, context: MiddlewareContext[mt.ListResourceTemplatesRequest], call_next: CallNext[mt.ListResourceTemplatesRequest, Sequence[ResourceTemplate]]) -> Sequence[ResourceTemplate]

Filter resource templates/list response based on auth checks.

on_list_prompts

on_list_prompts(self, context: MiddlewareContext[mt.ListPromptsRequest], call_next: CallNext[mt.ListPromptsRequest, Sequence[Prompt]]) -> Sequence[Prompt]

Filter prompts/list response based on auth checks.

on_get_prompt

on_get_prompt(self, context: MiddlewareContext[mt.GetPromptRequestParams], call_next: CallNext[mt.GetPromptRequestParams, PromptResult]) -> PromptResult

Check auth before prompt render.