MCP Server Authorization

Model Context Protocol (MCP) is the protocol AI applications (Claude, ChatGPT, Cursor and similar hosts) use 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, revision 2025-11-25, including OAuth 2.1, protected resource metadata (the discovery document an MCP server publishes so clients can find its authorization server), resource indicators (the resource parameter that pins a token to one server), the authorization-server discovery document, the issuer identifier in the authorization response (iss), and Client ID Metadata Documents (a client identifies itself with a URL to a metadata file instead of registering first) — the spec's preferred client registration mechanism. It also covers the accepted spec enhancements: SEP-835 (default scopes advertised in the 401 challenge), SEP-837 (application_type validation in dynamic client registration), SEP-2350 (incremental scope consent on step-up), SEP-2351 (standardized well-known URI suffix), and SEP-2352 (registration-credential-to-issuer binding).

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
Protected resource metadata	How MCP clients discover the authorization server for an MCP server
Resource indicators	Binding tokens to a specific MCP server audience
Discovery document	Discovering LumoAuth's endpoints
Dynamic client registration	MCP clients can register themselves through the API
Issuer identifier in the response	The iss parameter on the redirect back, which prevents mix-up attacks
Client ID metadata documents	URL-based client identity, preferred by MCP 2025-11-25

The exact specifications are listed in Standards used on this page.

Quickstart

To secure an MCP server with LumoAuth:

1. Register your MCP server in the Organization Portal under AI Agents → MCP servers (click Register MCP server).
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 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. The caller needs the settings.manage permission; an API key additionally needs the mcp:read scope. 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
• Client ID Metadata Documents — URL-based client registration

Standards used on this page

Plain name	Standard
Protected resource metadata	RFC 9728
Resource indicators	RFC 8707
Discovery document	RFC 8414
Issuer identifier in the response	RFC 9207
Client ID metadata documents	OAuth Client ID Metadata Document (draft)
Dynamic client registration	RFC 7591
Model Context Protocol (MCP) authorization	MCP Authorization specification

See the standards reference for what each one covers and how LumoAuth uses it.