Secured MCP Server with Spring AI

A demonstration of securing a Model Context Protocol (MCP) server using Spring Authorization Server and GitHub OAuth2. Users authenticate with GitHub, receive a JWT token, and use it to call secured MCP tools.

Based on the article by Daniel Garnier-Moiroux: https://spring.io/blog/2025/09/30/spring-ai-mcp-server-security

Architecture

┌─────────────┐
│   GitHub    │ (Identity Provider)
└──────┬──────┘
       │
       ▼
┌────────────────────────┐
│  Authorization Server  │ (Port 9000)
│  - GitHub OAuth Login  │
│  - Issues JWT tokens   │
└──────┬─────────────────┘
       │
       ▼
┌─────────────┐  Authorization: Bearer    ┌──────────────┐
│ MCP Client  │──────────────────────────────► │  MCP Server  │ (Port 8080)
└─────────────┘                                │  - 2 Tools   │
                                               └──────────────┘

Project Structure

mcps/
├── pom.xml                                   # Parent POM
├── mvnw                                      # Maven wrapper
│
├── authorization-server/                     # Port 9000
│   └── src/main/java/dev/danvega/authserver/
│       ├── AuthServerApplication.java        # Main application
│       ├── SecurityConfig.java               # OAuth2 + GitHub login
│       └── application.yml                   # Configuration
│
└── mcp-server/                               # Port 8080
    └── src/main/java/dev/danvega/mcps/
        ├── Application.java                  # Main application
        ├── McpServerSecurityConfig.java      # JWT validation
        └── McpToolsService.java              # MCP tools (echo, getCurrentUser)

Quick Start

1. Prerequisites

• Java 21+
• Maven 3.6+
• GitHub account

2. Create a GitHub OAuth App

1. Go to GitHub Developer Settings
2. Create a New OAuth App:
   • Application name: MCP Authorization Server
   • Homepage URL: http://localhost:9000
   • Callback URL: http://localhost:9000/login/oauth2/code/github
3. Save the Client ID and Client Secret

3. Set Environment Variables

export GITHUB_CLIENT_ID="your-github-client-id"
export GITHUB_CLIENT_SECRET="your-github-client-secret"

4. Build and Run

# Build both modules
./mvnw clean install

# Terminal 1: Start Authorization Server (must start first!)
./mvnw spring-boot:run -pl authorization-server

# Terminal 2: Start MCP Server
./mvnw spring-boot:run -pl mcp-server

The authorization server runs on port 9000, MCP server on port 8080.

Testing with MCP Inspector

The MCP Inspector tool provides an easy way to test the complete OAuth2 flow and interact with your secured MCP server.

Available MCP Tools

1. echo - Echo back a message with timestamp

{"message": "Hello"}

2. getCurrentUser - Get authenticated user information

{}

Key Features

Authorization Server (Port 9000)

• GitHub OAuth2 federated login
• Issues JWT access tokens (15-minute lifetime)
• Refresh tokens (1-day lifetime)
• Standard OAuth2/OIDC endpoints

MCP Server (Port 8080)

• JWT validation using JWKS from auth server
• Audience claim validation
• Two secured MCP tools
• Stateless architecture

Useful Endpoints

# Authorization server metadata
curl http://localhost:9000/.well-known/oauth-authorization-server

# JWKS (public keys for JWT validation)
curl http://localhost:9000/oauth2/jwks

Configuration Details

The MCP client is pre-registered with these credentials:

• Client ID: mcp-server
• Client Secret: secret
• Scopes: openid, profile, email, mcp.server, mcp.tools

Token lifetimes are configured in authorization-server/src/main/resources/application.yml:

• Access tokens: 15 minutes
• Refresh tokens: 1 day
• Authorization codes: 5 minutes

Troubleshooting

401 Unauthorized?

• Ensure auth server is running first (port 9000)
• Check your token hasn’t expired (15-minute lifetime)
• Get a fresh token if needed

GitHub OAuth not working?

• Verify callback URL: http://localhost:9000/login/oauth2/code/github
• Check GITHUB_CLIENT_ID and GITHUB_CLIENT_SECRET are set

References

• Spring AI MCP Server Security Article
• Spring Authorization Server Docs
• Model Context Protocol Specification