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M
MCP Oauth2 Proxy
by @risedphantom
GitHub Repo(1 stars)

HTTP reverse proxy for MCP servers that acts as an OAuth2 Authorization Server facade with Keycloak as the backing identity provider.

Created 4/2/2026
Updated about 3 hours ago
README
View Source
Repository documentation and setup instructions

mcp-oauth2-proxy

HTTP reverse proxy for MCP (Model Context Protocol) servers that acts as an OAuth2 Authorization Server facade with Keycloak as the backing identity provider.

The proxy handles the full MCP authorization lifecycle:

  • RFC 9728 Protected Resource Metadata discovery
  • RFC 8414 Authorization Server Metadata
  • RFC 7591 Dynamic Client Registration
  • OAuth2 Authorization Code flow with PKCE (S256)
  • OIDC discovery from Keycloak for token/authorization endpoints
  • Configurable header mutations on proxied requests
  • SSE (Server-Sent Events) streaming passthrough

How It Works

                         ┌──────────────────────────────────┐
                         │        mcp-oauth2-proxy          │
                         │                                  │
MCP Client ──Bearer──►   │  AuthMiddleware (JWT validation) │
                         │  Header Mutations (add/remove)   │ ──►  Upstream MCP Server
                         │  ReverseProxy (SSE streaming)    │
                         │                                  │
                         │  OAuth2 AS Facade:               │
                         │   /oauth/register                │
                         │   /oauth/authorize  ◄──────────► │ ──►  Keycloak (OIDC)
                         │   /oauth/callback                │
                         │   /oauth/token                   │
                         └──────────────────────────────────┘

OAuth2 Authorization Code flow:

  1. MCP client discovers the proxy via GET /.well-known/oauth-protected-resource
  2. Client registers dynamically via POST /oauth/register (gets client_id + client_secret)
  3. Client starts authorization via GET /oauth/authorize with PKCE S256
  4. Proxy redirects to Keycloak — user authenticates
  5. Keycloak redirects back to GET /oauth/callback — proxy exchanges KC code for tokens
  6. Proxy redirects client back with a proxy-issued authorization code
  7. Client exchanges the code via POST /oauth/token (PKCE verified) — receives Keycloak tokens
  8. Client uses the access token as Authorization: Bearer on subsequent proxy requests

Proxied requests pass through AuthMiddleware (Bearer JWT validation — signature and expiration) and configurable header mutations before reaching the upstream server.

Quick Start

Prerequisites

  • Go 1.24+
  • A Keycloak instance with a configured realm and client

Build and Run

# Build
make build

# Run with example config
make serve

# Or run directly
./mcp-oauth2-proxy serve --config config/config.yaml

Docker

# Build image
make docker-build

# Run
docker run -v $(pwd)/config.yaml:/app/config.yaml mcp-oauth2-proxy:latest

Configuration

Configuration is loaded from YAML, with support for environment variable overrides (prefix MCP_OAUTH2_PROXY_).

Minimal Example

upstream:
  url: http://localhost:3000

auth:
  baseUrl: https://mcp-proxy.example.com
  authorizationServers:
    - https://mcp-proxy.example.com
  issuerUrl: https://auth.example.com/realms/myrealm
  clientId: mcp-proxy
  clientSecret: secret

Full Example

server:
  listenAddress: ":8080"
  readTimeout: "30s"
  writeTimeout: "0s"       # 0 = no timeout, required for SSE
  idleTimeout: "120s"

upstream:
  url: http://localhost:3000

headers:
  mutations:
    - action: set-x-forwarded
    - action: remove
      name: X-Unwanted-Header
    - action: add
      name: X-Forwarded-By
      value: mcp-oauth2-proxy
    - action: add
      name: X-Original-Host
      valueFrom:
        requestHeader: Host
    - action: add
      name: X-Query-Token
      valueFrom:
        queryParameter: token
    - action: add
      name: X-Auth-Header
      valueFrom:
        authorizationHeader: true

auth:
  baseUrl: https://mcp-proxy.example.com
  authorizationServers:
    - https://mcp-proxy.example.com
  scopesSupported:
    - mcp:read
    - mcp:write
  oidcScopes:
    - openid
    - profile
    - email
    - groups
  issuerUrl: https://auth.example.com/realms/myrealm
  clientId: mcp-proxy
  clientSecret: secret
  clientTtl: "24h"         # TTL for dynamically registered clients
  sessionTtl: "10m"        # TTL for in-progress auth flows
  codeTtl: "5m"            # TTL for authorization codes

Configuration Reference

| Field | Required | Default | Description | |---|---|---|---| | server.listenAddress | No | :8080 | HTTP listen address | | server.readTimeout | No | 30s | HTTP read timeout | | server.writeTimeout | No | 0s | HTTP write timeout (0 for SSE) | | server.idleTimeout | No | 120s | HTTP idle timeout | | upstream.url | Yes | — | Upstream MCP server URL (absolute) | | headers.mutations | No | [] | Ordered list of header mutations | | auth.baseUrl | Yes | — | Proxy's public base URL (OAuth2 issuer) | | auth.authorizationServers | No | [baseUrl] | List of authorization server URLs (defaults to baseUrl) | | auth.issuerUrl | Yes | — | Keycloak realm URL for OIDC discovery | | auth.clientId | Yes | — | Keycloak client ID | | auth.clientSecret | Yes | — | Keycloak client secret | | auth.scopesSupported | No | [] | Scopes advertised in metadata | | auth.oidcScopes | No | [] | Scopes to request from Keycloak | | auth.clientTtl | No | 24h | TTL for dynamically registered clients | | auth.sessionTtl | No | 10m | TTL for in-progress auth flows | | auth.codeTtl | No | 5m | TTL for authorization codes |

Header Mutations

Mutations are applied in order during request rewriting:

| Action | Fields | Description | |---|---|---| | remove | name | Remove header by name | | add | name, value or valueFrom | Set header from static value or dynamic source | | set-x-forwarded | (none) | Add X-Forwarded-For, X-Forwarded-Proto, X-Forwarded-Host |

valueFrom sources (exactly one):

  • requestHeader: <name> — copy from incoming request header
  • queryParameter: <name> — extract from URL query parameter
  • authorizationHeader: true — extract Bearer token value

Environment Variables

All config fields can be overridden via environment variables with prefix MCP_OAUTH2_PROXY_. Dots are replaced with _; camelCase field names are matched case-insensitively:

export MCP_OAUTH2_PROXY_UPSTREAM_URL=http://localhost:3000
export MCP_OAUTH2_PROXY_AUTH_ISSUERURL=https://auth.example.com/realms/myrealm
export MCP_OAUTH2_PROXY_AUTH_CLIENTID=mcp-proxy
export MCP_OAUTH2_PROXY_AUTH_CLIENTSECRET=secret

API Endpoints

Health & Readiness

curl http://localhost:8080/healthz   # → "ok"
curl http://localhost:8080/readyz    # → "ok"

OAuth2 Discovery

# RFC 9728 Protected Resource Metadata
curl http://localhost:8080/.well-known/oauth-protected-resource

# RFC 8414 Authorization Server Metadata
curl http://localhost:8080/.well-known/oauth-authorization-server

Dynamic Client Registration (RFC 7591)

curl -X POST http://localhost:8080/oauth/register \
  -H "Content-Type: application/json" \
  -d '{
    "redirect_uris": ["http://localhost:3000/callback"],
    "client_name": "my-mcp-client",
    "grant_types": ["authorization_code"]
  }'

Authorization & Token Exchange

# Start authorization (browser redirect)
GET /oauth/authorize?response_type=code&client_id=...&redirect_uri=...&code_challenge=...&code_challenge_method=S256&state=...&scope=...

# Exchange code for tokens
curl -X POST http://localhost:8080/oauth/token \
  -d "grant_type=authorization_code&code=...&client_id=...&client_secret=...&redirect_uri=...&code_verifier=..."

Kubernetes Deployment

A Helm chart is provided in deploy/helm/.

# Install
helm install mcp-oauth2-proxy deploy/helm \
  -n mcp-oauth2-proxy --create-namespace \
  -f values-production.yaml

# Debug template rendering
make helm-debug

The chart includes:

  • Deployment with liveness (/healthz) and readiness (/readyz) probes
  • Service (ClusterIP, port 8080)
  • ConfigMap for proxy configuration (mounted at /app/config.yaml)
  • ServiceAccount with auto-mount
  • Security context: readOnlyRootFilesystem, runAsNonRoot, drop ALL capabilities

Development

make build           # Build binary
make test            # Run tests
make test-coverage   # Tests with coverage report
make lint            # Run golangci-lint
make fmt             # Format code
make deps            # Download and tidy dependencies

CLI Flags

mcp-oauth2-proxy serve --config <path>     # Config file path (default: config.yaml)
mcp-oauth2-proxy serve --log-level DEBUG   # Log level: DEBUG, INFO, WARN, ERROR, FATAL, PANIC
mcp-oauth2-proxy serve --log-format json   # Log format: text, json
mcp-oauth2-proxy version                   # Print version info

CI/CD

GitLab CI pipeline (.gitlab-ci.yml):

  • Docker image: built and pushed on semver tags (e.g., 1.0.0)
  • Helm chart: packaged and pushed on helm-* tags (e.g., helm-1.0.0)
  • Includes shared CI templates for multi-arch builds, security scanning, and Helm publishing
Quick Setup
Installation guide for this server

Installation Command (package not published)

git clone https://github.com/risedphantom/mcp-oauth2-proxy
Manual Installation: Please check the README for detailed setup instructions and any additional dependencies required.

Cursor configuration (mcp.json)

{ "mcpServers": { "risedphantom-mcp-oauth2-proxy": { "command": "git", "args": [ "clone", "https://github.com/risedphantom/mcp-oauth2-proxy" ] } } }