Spring AI MCP Gateway (Streamable HTTP + OAuth 2.1)

Reference project that shows, end‑to‑end, how to configure:

• MCP clients: SSE (e.g., JetBrains Copilot) and stdio (Docker images mcp/*).
• MCP server: SSE and Streamable HTTP (the gateway exposes /mcp).
• Security modes: no auth, OAuth 2.1 with Client Credentials, and Authorization Code + PKCE (public client).

The goal is educational and practical: expose a local development environment so that ChatGPT can interact with it through a simple MCP gateway. We also document how to publish it to the Internet using Cloudflare Tunnels with path‑based routing—no reverse proxy in front of our services—and how to configure the ChatGPT Connector.

Important: this is not meant to be a production‑grade gateway. It’s a hands‑on reference that connects a few pieces to deliver a very visual use‑case: “Let ChatGPT operate my dev environment”. For an operational, hardened gateway, see docker-mcp-gateway.md.

Modules remain the same:

• auth-server/ – OAuth 2.1 Authorization Server (JWT issuer) on port 9090.
• mcp-gateway/ – Spring AI MCP server/client acting as a Resource Server on port 8080.

The public MCP endpoint is exposed at https://<your-domain>/mcp (through the tunnel) and protected with Bearer tokens obtained by ChatGPT through the OAuth flow against the Authorization Server at https://<your-domain>.

Scenarios & Branches

This repository uses branches to illustrate the evolution and the different auth modes:

• NO_AUTH_SSE — SSE without security. Minimal Spring AI setup and wiring. Github Copilot using the gateway at http://localhost:8080/sse.
• OAUTH2.1_STREAMABLE — Streamable HTTP + OAuth 2.1 with Client Credentials (local issuer).
• OAUTH2.1_CHATGPT_TUNNELS — ChatGPT Connectors + Cloudflare Tunnels + OAuth 2.1 (Authorization Code + PKCE, this branch)
  • Streamable HTTP at /mcp (Gateway on 8080). Multiple tools exposed through the same endpoint.
  • Public client (no secret), ChatGPT completes the OAuth flow and manages refresh tokens.
  • Single public hostname via Cloudflare Tunnel with path‑based routing. Resource Server validates JWTs from the public issuer.

What Changed From OAUTH2.1_STREAMABLE to OAUTH2.1_CHATGPT_TUNNELS

• Authentication flow: from Client Credentials → Authorization Code + PKCE with a public client (no secret).
• Issuer and URLs: from http://localhost:9090 → public https://<your-domain> through Cloudflare Tunnel.
• ChatGPT integration: the connector completes the OAuth flow and manages token refresh automatically.
• Resource Server keeps Streamable HTTP at /mcp and validates JWTs from the public issuer.

Project Structure

• Parent aggregator POM (pom.xml, packaging pom).
• Modules:
  • auth-server/ – Authorization server configuration and keys. Config: auth-server/src/main/resources/application.yml (port 9090).
  • mcp-gateway/ – MCP Gateway server/client and security. Config: mcp-gateway/src/main/resources/application.yml (port 8080).

Build

• Build all modules: mvn -q clean package

Run (Local)

1. Start the Authorization Server (port 9090):

• mvn -q -pl auth-server spring-boot:run

1. Start the MCP Gateway (port 8080):

• mvn -q -pl mcp-gateway spring-boot:run

Cloudflare Tunnel

• cloudflared tunnel run mcp-gateway # For Cloudflare Tunnel setup and path‑based routing, see CLOUDFLARE.md.

Traffic will be routed in my case, from https://dev.omarall.es to our local processes.

Register the Gateway in ChatGPT (OAuth 2.1 + PKCE)

See CHATGPT for detailed steps.

⚠️ Security Notes

This repository is a learning and integration reference, just that. Its goal is to demonstrate how to connect and configure Spring AI + MCP + OAuth 2.1.

Important security notes:

• Do not use demo credentials in production. The default in-memory user (omar/secret) is for local testing only.

• CORS and CSRF are relaxed for simplicity. Always restrict origins, allowed methods, and re-enable CSRF when building real deployments.

• Scopes (mcp:read, mcp:write) are defined for illustration only — enforce real scope-based authorization when applicable.

• Use HTTPS with verified domains and Zero Trust policies if publishing externally.

Useful References

• https://spring.io/blog/2025/09/16/spring-ai-mcp-intro-blog
• https://spring.io/blog/2025/09/19/spring-ai-1-1-0-M2-mcp-focused
• https://www.danvega.dev/blog/cyc-mcp-server-spring-ai
• https://github.com/spring-ai-community/mcp-security/
• https://spring.io/blog/2025/09/30/spring-ai-mcp-server-security
• https://blog.christianposta.com/understanding-mcp-authorization-step-by-step/
• https://blog.christianposta.com/understanding-mcp-authorization-step-by-step-part-two/
• https://blog.christianposta.com/understanding-mcp-authorization-step-by-step-part-three/
• https://blog.christianposta.com/understanding-mcp-authorization-with-dynamic-client-registration/
• https://blog.christianposta.com/api-keys-are-a-bad-idea-for-enterprise-llm-agent-and-mcp-access/