MCP Keycloak Resource Server (mcp-keycloak)

This project implements a Model Context Protocol (MCP) protected Resource Server secured by an OAuth 2.0 Authorization Server (Keycloak) using Token Introspection (RFC 7662).

The server is built with the Python mcp SDK using the FastMCP framework, showcasing how to restrict access to MCP tools by requiring a valid Bearer token.

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Architecture Overview

+--------------------+        1. Request Token         +--------------------+
|                    | ------------------------------> |                    |
|     MCP Client     |                                 |      Keycloak      |
| (e.g., test_client)| <------------------------------ | (Auth Server, :8080)
|                    |         2. Access Token         +--------------------+
+--------------------+                                           ^
          |                                                      |
          | 3. Call Tool (with Bearer Token)                     |
          v                                                      | 4. Introspect
+--------------------+                                           |    Token
|     MCP Server     | ------------------------------------------+
| (Resource, :3000)  | <------------------------------------------
+--------------------+            5. Active: True/False

1. Keycloak (Authorization Server): Serves on port 8080. It handles client credential grants and token introspection. A pre-configured database is included in the project directory (keycloak_data/) to make spin-up seamless.
2. MCP Resource Server (Resource Server): Built with FastMCP, running on port 3000. When a client calls a protected tool, the server intercepts the request and validates the Authorization: Bearer <token> header against Keycloak's introspection endpoint.
3. Token Verifier (IntrospectionTokenVerifier): Implements standard OAuth 2.0 token introspection (RFC 7662). It validates token activity, resource/audience restrictions (aud), scope limits, and expiration times.

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Prerequisites

• Python: Version 3.12 or higher (compatible with uv)
• Docker & Docker Compose: To run Keycloak

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Pre-Configured Keycloak Clients

The embedded Keycloak database is pre-configured with three OAuth 2.0 clients within the master realm. The full, exact JSON configuration of these clients is exported and available in the keycloak_config.json file.

These clients use the Client Credentials Grant flow (via Service Accounts) and are configured with specific client secrets, scopes, and audience mappers:

1. mcp-client (Primary Testing Client)

• Client ID: mcp-client
• Client Secret: 64gq3p8y3siZKZoKH6X9Bq2oqIPfukBZYMnmyCVCJw1QgjfNzdympB0eaZ1aXtFl0yNUWzGr3S7Gov3gR4kLfe
• Authentication Flow: Client Credentials (Service Account enabled)
• Assigned Scopes: mcp:tools
• Audience Mappers:
  • mcp-server
  • http://localhost:3000 (derived resource server URL)

2. mcp-client-2 (Alternative Testing Client)

• Client ID: mcp-client-2
• Client Secret: FebOB24OaG3F4J9dMZPoZ7qhzQvUKQ5HgJ6IbQ6yXQBd5tg88f8tPSEA0aUGK9AuEebxHRBwsPdLuDjQpiLFhR
• Authentication Flow: Client Credentials (Service Account enabled)
• Assigned Scopes: mcp:tools
• Audience Mappers:
  • mcp-server
  • http://localhost:3000

3. mcp-server (Resource Server Introspection)

• Client ID: mcp-server
• Client Secret: 5XflSzJJrvQD8iNz4t7RMI4i9rNvdnLQs5PSo8EMGkfUDKr02SjaPs4fKA9kWNO1G06nhDzTHMeHrnz9H4h5ut
• Authentication Flow: Client Credentials (Service Account enabled) — used by the Resource Server to authenticate introspection requests.
• Assigned Scopes: mcp:tools
• Audience Mappers:
  • mcp-server
  • http://localhost:3000

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Installation & Setup

1. Start Keycloak

Run the Keycloak container in development mode using the provided docker-compose.yml:

docker compose up -d

Keycloak starts on http://127.0.0.1:8080. Admin credentials are:

• Username: admin
• Password: admin

Note: The container mounts ./keycloak_data, preserving the pre-configured realm, clients (mcp-server, mcp-client, and mcp-client-2), and settings.

2. Install Project Dependencies

If you are using uv:

uv sync

Alternatively, standard pip can be used:

pip install -e .

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Running the Server

Start the MCP Resource Server:

uv run main.py

By default, the server starts on http://localhost:3000 using the streamable-http transport (supporting Streamable HTTP MCP communication).

Server Configuration

Configuration options can be customized via environment variables defined in config.py:

Environment Variable	Default Value	Description
HOST	localhost	MCP Server hostname
PORT	3000	MCP Server port
AUTH_HOST	localhost	Keycloak server host
AUTH_PORT	8080	Keycloak server port
AUTH_REALM	master	Keycloak Realm to use
OAUTH_CLIENT_ID	mcp-server	Client ID the Resource Server uses for Introspection
OAUTH_CLIENT_SECRET	5XflSzJJrv...	Client Secret for Introspection client
MCP_SCOPE	mcp:tools	Scope required to invoke the MCP tools
OAUTH_STRICT	false	Enable strict OAuth validations
TRANSPORT	streamable-http	MCP Transport protocol (streamable-http or sse)

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Secure MCP Tools Provided

The server registers two secure arithmetic tools:

1. add_numbers

   • Arguments: a: float, b: float
   • Operation: Adds two numbers together.
   • Output: Returns JSON containing parameters, sum result, and timestamp.

2. multiply_numbers

   • Arguments: x: float, y: float
   • Operation: Multiplies two numbers.
   • Output: Returns JSON containing parameters, product result, and timestamp.

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Testing with the Test Client

A CLI-based test client (test_client.py) is included to simulate MCP client interactions.

1. View Help Options

To see all available CLI flags:

uv run test_client.py --help

2. Automatically Fetch Token & List Secure Tools

To retrieve a client token via Keycloak's client credentials flow (using client credentials configured for mcp-client) and list the available tools on the MCP server:

uv run test_client.py --fetch-token

To use the alternative mcp-client-2 client, specify the client credentials flags:

uv run test_client.py --fetch-token --client-id mcp-client-2 --client-secret FebOB24OaG3F4J9dMZPoZ7qhzQvUKQ5HgJ6IbQ6yXQBd5tg88f8tPSEA0aUGK9AuEebxHRBwsPdLuDjQpiLFhR

3. Call a Protected Tool

To execute a secure tool using an automatically fetched token:

Addition Example:

uv run test_client.py --fetch-token --call add_numbers --args '{"a": 15.5, "b": 24.5}'

Multiplication Example:

uv run test_client.py --fetch-token --call multiply_numbers --args '{"x": 6.0, "y": 7.0}'

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Technical Details

Token Validation Rules (token_verifier.py)

When an incoming MCP request is received, IntrospectionTokenVerifier.verify_token(token) validates:

• HTTP status: The introspection request successfully responds with an HTTP 200 status.
• Activity: The response JSON includes "active": true.
• Audience (aud): The audience claim matches the resource server URL (derived dynamically, e.g., http://localhost:3000/).
• Scopes: Validated to ensure the client has the required mcp:tools scope.