A fast, fully configurable, in-memory OAuth 2.0 + OpenID Connect authorization server for testing, zero-HTTP mode and DCR support for testing auth flow in MCP Servers and MCP Clients.

This server was developed with the purpose of supporting testing and development of the rust-mcp-sdk, but it works perfectly as a general-purpose auth mocking in any Rust (or non-Rust) project , unit tests, integration suites, local dev, or quick prototypes.
Refer to Key Features to find out more.

⚠️ For testing/development only

• In-memory storage (not persistent)
• No rate limiting or attack protection
• Use in test suites, CI/CD, local development

Purpose

This server implements all major OAuth 2.0 flows and OpenID Connect core features in-memory, making it ideal for:

• Testing OAuth clients (web, mobile, SPA, backend)
• Specifically tailored for testing authentication flow MCP Servers and Clients, with DCR support
• End-to-end flow validation
• Local development
• Integration testing of authorization flows
• Local development against a real OAuth provider
• Demonstrating OAuth concepts
• CI/CD pipeline validation

Supported Standards

Key Features

• Dynamic Client Registration (DCR) (POST /register) with full metadata support
• Authorization Code Flow with PKCE (/authorize, /token)
• Refresh Token Flow with rotation and revocation
• Client Credentials Grant
• Device Code Flow (RFC 8628) (/device/code, /device/token)
• JWT Access Tokens signed with RS256 (auto-generated RSA key pair)
• ID Tokens with at_hash, c_hash, nonce, standard claims
• Token Introspection (POST /introspect) with expiration checking
• Token Revocation (POST /revoke)
• OpenID Connect Discovery (.well-known/openid-configuration)
• JWKS Endpoint (.well-known/jwks.json)
• UserInfo Endpoint (GET /userinfo)
• In-memory stores (clients, codes, tokens, device codes) - no external DB required
• Background TTL cleanup for expired tokens/codes
• Full error handling with redirect errors and JSON error responses
• State parameter (required by default, configurable)
• Scope, redirect_uri validation
• Authorization parameters: prompt, max_age, claims, ui_locales, response_mode
• Configurable via YAML/TOML files or environment variables

Endpoints

Note: /token endpoint supports all OAuth2 grant types: Authorization Code, Refresh Token, Client Credentials. The Device Code flow uses separate endpoints (/device/code and /device/token) since it's a polling mechanism, but the main /token endpoint handles the three most common grants.

In-Memory Stores

• clients: HashMap<String, Client> - registered clients
• codes: HashMap<String, AuthorizationCode> - short-lived auth codes
• tokens: HashMap<String, Token> - access tokens (JWTs)
• refresh_tokens: HashMap<String, Token> - refresh token mapping
• device_codes: HashMap<String, DeviceAuthorization> - device code flow state

Security & Testing

• No persistence - perfect for isolated tests
• Auto-generated RSA key pair on startup
• PKCE verification (S256 and plain)
• Token revocation propagation
• Expiration enforcement (configurable TTL)
• Background cleanup of expired tokens/codes
• Scope and redirect_uri validation
• State parameter (required by default, configurable)
• ID Token security (at_hash, c_hash validation)
• Configurable token expiration times

Run as a Standalone Binary (Great for Manual Testing & Debugging)

You can run the server directly from your terminal - no code required.

1. Install it globally using one of the following methods:

• Cargo

  cargo install oauth2-test-server
  

• Shell script

  curl --proto '=https' --tlsv1.2 -LsSf https://github.com/rust-mcp-stack/oauth2-test-server/releases/download/v0.2.3/oauth2-test-server-installer.sh | sh
  

• PowerShell script

  powershell -ExecutionPolicy Bypass -c "irm https://github.com/rust-mcp-stack/oauth2-test-server/releases/download/v0.2.3/oauth2-test-server-installer.ps1 | iex"
  

• Homebrew

  brew install rust-mcp-stack/tap/oauth2-test-server
  

• NPM

  npm i -g @rustmcp/oauth2-test-server@latest
  

  The npm package is provided for convenience. It runs the same underlying Rust binary but can be installed and used as a standard npm package.

• Download Binaries

2. Start the server

oauth2-test-server

You’ll see:

OAuth Test Server running on http://127.0.0.1:8090/
 • Discovery: http://127.0.0.1:8090/.well-known/openid-configuration
 • Jwks: http://127.0.0.1:8090/.well-known/jwks.json
 • Authorize: http://127.0.0.1:8090/authorize
 • Token: http://127.0.0.1:8090/token
 • Device Code: http://127.0.0.1:8090/device/code
 • Device Token: http://127.0.0.1:8090/device/token
 • Register: http://127.0.0.1:8090/register
 • Introspection: http://127.0.0.1:8090/introspect
 • UserInfo: http://127.0.0.1:8090/userinfo
 • Revoke: http://127.0.0.1:8090/revoke

Quick test with curl:

# Register a client
curl -X POST http://localhost:8090/register -H "Content-Type: application/json" -d '{
  "redirect_uris": ["http://localhost:8090/callback"],
  "grant_types": ["authorization_code"],
  "response_types": ["code"],
  "scope": "openid profile email"
}'

Configuration

The server is configured via IssuerConfig.

Default User

The server uses a hardcoded user identity for all authorization requests. By default this is "test-user-123".

Set it programmatically:

use oauth2_test_server::IssuerConfig;

let config = IssuerConfig {
    default_user_id: "alice".into(),
    port: 0,
    ..Default::default()
};
let server = OAuthTestServer::start_with_config(config).await;

Or, when using the library in your own tests, load from environment variables (OAUTH_*) or a YAML/TOML file:

// From environment variables (requires "config" feature)
let config = IssuerConfig::from_env()?;

// From a YAML or TOML file (requires "config" feature)
let config = IssuerConfig::from_file("path/to/config.yaml")?;

Note: The standalone binary (oauth2-test-server) does not currently accept CLI flags or config files. Use the library API for custom configuration.

A complete sample config file with all options and their defaults can be found at config.sample.yaml.

All Configuration Options

Loading Order

1. Programmatic IssuerConfig (highest priority)
2. Environment variables (OAUTH_*)
3. YAML/TOML config file (detected by extension: .yaml, .yml, .toml)
4. Built-in defaults (lowest priority)

The from_env and from_file methods are available when the config feature is enabled (included by default).

How to Use in Tests

Quick Start

#[tokio::test]
async fn quick_start() {
    let server = oauth2_test_server::OAuthTestServer::start().await;
    println!("server: {}", server.base_url());
    
    let client = server.register_client(serde_json::json!({
        "scope": "openid",
        "redirect_uris": ["http://localhost:8080/callback"],
        "client_name": "rust-mcp-sdk"
    })).await;
    
    // Generate a token directly
    let token = server.generate_token(&client, 
        server.jwt_options().user_id("rustmcp").build()
    ).await;
    
    assert_eq!(token.access_token.split('.').count(), 3);
}

Authorization Code Flow with PKCE

#[tokio::test]
async fn auth_code_flow_with_pkce() {
    let server = OAuthTestServer::start().await;
    
    let client = server.register_client(serde_json::json!({
        "scope": "openid profile email",
        "redirect_uris": ["http://localhost:8080/callback"],
        "client_name": "test-client"
    })).await;
    
    let pkce = server.pkce_pair();
    
    let auth_url = server.authorize_url(&client, AuthorizeParams::new()
        .redirect_uri("http://localhost:8080/callback")
        .scope("openid profile")
        .nonce("test-nonce-123")
        .pkce(pkce.clone())
    );
    
    let code = server.approve_consent(&auth_url, "test-user").await;
    
    let token_response = server.exchange_code(&client, &code, Some(&pkce)).await;
    
    assert!(token_response.get("access_token").is_some());
    assert!(token_response.get("id_token").is_some()); // ID token with openid scope
    assert!(token_response.get("refresh_token").is_some());
}

Complete Auth Flow (One-Liner)

#[tokio::test]
async fn complete_auth_flow() {
    let server = oauth2_test_server::OAuthTestServer::start().await;
    
    let client = server.register_client(serde_json::json!({
        "scope": "openid profile email",
        "redirect_uris": ["http://localhost:8080/callback"],
        "client_name": "test-client"
    })).await;
    
    // Complete flow in one call
    let token = server.complete_auth_flow(
        &client,
        AuthorizeParams::new()
            .redirect_uri("http://localhost:8080/callback")
            .scope("openid profile"),
        "test-user"
    ).await;
    
    assert!(token.get("access_token").is_some());
    assert!(token.get("id_token").is_some());
}

Device Code Flow

#[tokio::test]
async fn device_code_flow() {
    let server = oauth2_test_server::OAuthTestServer::start().await;
    
    // Register client with device_code grant
    let client = server.register_client(serde_json::json!({
        "scope": "openid profile",
        "grant_types": ["urn:ietf:params:oauth:grant-type:device_code"],
        "client_name": "device-client"
    })).await;
    
    // Complete device flow in one call
    let token = server.complete_device_flow(&client, "openid profile", "device-user").await;
    
    assert!(token.get("access_token").is_some());
    assert!(token.get("refresh_token").is_some());
}

Token Introspection & Revocation

#[tokio::test]
async fn token_introspection_and_revoke() {
    let server = oauth2_test_server::OAuthTestServer::start().await;
    
    let client = server.register_client(serde_json::json!({
        "scope": "openid",
        "redirect_uris": ["http://localhost:8080/callback"],
    })).await;
    
    let pkce = server.pkce_pair();
    let auth_url = server.authorize_url(&client, AuthorizeParams::new()
        .redirect_uri("http://localhost:8080/callback")
        .scope("openid")
        .pkce(pkce.clone())
    );
    let code = server.approve_consent(&auth_url, "test-user").await;
    let token = server.exchange_code(&client, &code, Some(&pkce)).await;
    
    let access_token = token["access_token"].as_str().unwrap();
    
    // Introspect token
    let introspection = server.introspect_token(&client, access_token).await;
    assert!(introspection["active"].as_bool().unwrap());
    
    // Revoke token
    server.revoke_token(&client, access_token).await;
    
    // Verify revoked
    let introspection_after = server.introspect_token(&client, access_token).await;
    assert!(!introspection_after["active"].as_bool().unwrap());
}

Custom Token Generation (for unit tests)

#[tokio::test]
async fn custom_token() {
    let server = oauth2_test_server::OAuthTestServer::start().await;
    
    let client = server.register_client(serde_json::json!({
        "scope": "openid profile email",
        "redirect_uris": ["http://localhost:8080/callback"]
    })).await;
    
    // Generate JWT directly with custom claims
    let jwt = server.generate_jwt(&client, 
        server.jwt_options()
            .user_id("custom-user")
            .scope("openid profile")
            .expires_in(7200)
            .build()
    );
    
    assert!(jwt.split('.').count() == 3);
}

Loading from Config File

#[tokio::test]
async fn with_config() {
    use oauth2_test_server::IssuerConfig;
    
    let config = IssuerConfig {
        require_state: false,
        port: 0,
        ..Default::default()
    };
    
    let server = OAuthTestServer::start_with_config(config).await;
    
    let client = server.register_client(serde_json::json!({
        "scope": "openid",
        "redirect_uris": ["http://localhost:8080/callback"],
    })).await;
    
    let token = server.generate_token(&client, 
        server.jwt_options().user_id("testuser").build()
    ).await;
    
    assert!(!token.access_token.is_empty());
}

Migration Guide

Upgrading from 0.1.x to 0.2.x

1. Methods are now async - Add .await:

// Before (0.1.x)
let client = server.register_client(json!({...}));
let token = server.generate_token(&client, options);

// After (0.2.x)
let client = server.register_client(json!({...})).await;
let token = server.generate_token(&client, options).await;

2. Accessor methods return Vec instead of Arc<RwLock<HashMap>>:

// Before (0.1.x)
assert_eq!(server.clients().read().iter().len(), 1);

// After (0.2.x)
assert_eq!(server.clients().await.len(), 1);

// Or for mutation (reset state between tests):
server.clear_all().await;