MCP Server Authorization

Model Context Protocol (MCP) is a protocol for LLM hosts (Claude, ChatGPT, Cursor) to discover and call external tools. MCP servers expose tools; MCP clients invoke them. When an MCP server exposes sensitive resources, it needs authorization to ensure only permitted clients and users can access it.

LumoAuth's role is to authorize those tool calls: register MCP servers as protected resources, configure scopes, and let LumoAuth serve as the OAuth 2.0 authorization server while AI applications act as OAuth clients.

Specifications implemented

This implementation follows the MCP Authorization specification (draft), including OAuth 2.1, RFC 9728 (Protected Resource Metadata), RFC 8707 (Resource Indicators), and RFC 8414 (Authorization Server Metadata).

Architecture

Key concepts

Roles

Role	Description	In LumoAuth
Authorization Server	Issues access tokens and handles user authentication	LumoAuth serves this role
Resource Server (MCP Server)	Hosts tools, resources, and prompts; validates Bearer tokens	Your registered MCP server
Client (MCP Client)	AI application that connects to MCP servers on behalf of users	Registered as an OAuth client in LumoAuth

Standards implemented

Standard	Purpose
OAuth 2.1	Core authorization framework with security best practices
RFC 9728	OAuth 2.0 Protected Resource Metadata — how MCP clients discover the authorization server
RFC 8707	Resource Indicators — binding tokens to specific MCP server audiences
RFC 8414	Authorization Server Metadata — discovering LumoAuth endpoints
RFC 7591	Dynamic Client Registration — MCP clients can self-register

Quickstart

To secure an MCP server with LumoAuth:

1. Register your MCP server in the Organization Portal under Developer > MCP Servers.
2. Configure your MCP server to return 401 Unauthorized with a WWW-Authenticate header pointing to LumoAuth's Protected Resource Metadata.
3. Validate tokens using LumoAuth's token introspection endpoint, verifying that the aud claim matches your server's Resource URI.

API endpoints

GET /orgs/{orgId}/api/v1/.well-known/oauth-protected-resource/mcp/{serverId} — Protected Resource Metadata (RFC 9728) for a specific MCP server. View details →

GET /orgs/{orgId}/api/v1/.well-known/oauth-protected-resource — root-level Protected Resource Metadata for the organization's MCP servers. View details →

GET /orgs/{orgId}/api/v1/mcp/servers — list all active MCP servers for an organization (requires Bearer token). View details →

GET /orgs/{orgId}/api/v1/mcp/servers/{serverId} — details of a specific MCP server including discovery URLs. View details →

GET / POST /orgs/{orgId}/api/v1/mcp/{serverId}/challenge — test the 401 challenge flow. Returns the WWW-Authenticate header for unauthenticated requests. View details →

Related

• MCP Authorization Flow — step-by-step OAuth 2.1 flow
• Protected Resource Metadata — discovery document details
• MCP Server Registration — register your MCP server