coder/docs/admin/integrations/oauth2-provider.md

OAuth2 Provider (Experimental)

Warning

The OAuth2 provider functionality is currently experimental and unstable. This feature:

• Is subject to breaking changes without notice
• May have incomplete functionality
• Is not recommended for production use
• Requires the oauth2 experiment flag to be enabled

Use this feature for development and testing purposes only.

Coder can act as an OAuth2 authorization server, allowing third-party applications to authenticate users through Coder and access the Coder API on their behalf. This enables integrations where external applications can leverage Coder's authentication and user management.

Requirements

• Admin privileges in Coder
• OAuth2 experiment flag enabled
• HTTPS recommended for production deployments

Enable OAuth2 Provider

Add the oauth2 experiment flag to your Coder server:

coder server --experiments oauth2

Or set the environment variable:

CODER_EXPERIMENTS=oauth2

Creating OAuth2 Applications

Method 1: Web UI

1. Navigate to Deployment Settings → OAuth2 Applications
2. Click Create Application
3. Fill in the application details:
   • Name: Your application name
   • Callback URL: https://yourapp.example.com/callback
   • Icon: Optional icon URL

Method 2: Management API

Create an application using the Coder API:

curl -X POST \
  -H "Authorization: Bearer $CODER_SESSION_TOKEN" \
  -H "Content-Type: application/json" \
  -d '{
    "name": "My Application",
    "callback_url": "https://myapp.example.com/callback",
    "icon": "https://myapp.example.com/icon.png"
  }' \
  "$CODER_URL/api/v2/oauth2-provider/apps"

Generate a client secret:

curl -X POST \
  -H "Authorization: Bearer $CODER_SESSION_TOKEN" \
  "$CODER_URL/api/v2/oauth2-provider/apps/$APP_ID/secrets"

Integration Patterns

Client Authentication Methods

Coder supports the following OAuth2 client authentication methods at the token endpoint (/oauth2/tokens):

• client_secret_basic (recommended): HTTP Basic authentication (RFC 6749 §2.3.1). The username is client_id and the password is client_secret.
• client_secret_post: Form-based authentication where client_id and client_secret are sent in the request body.

Coder supports both methods for compatibility; existing integrations using client_secret_post do not need to change.

If you use Dynamic Client Registration (RFC 7591) and omit token_endpoint_auth_method, clients default to client_secret_basic. To request client_secret_post, set token_endpoint_auth_method to client_secret_post in the registration request.

If client authentication fails, the token endpoint returns HTTP 401 with an OAuth2 invalid_client error and a WWW-Authenticate: Basic realm="coder" response header.

Standard OAuth2 Flow

1. Authorization Request: Redirect users to Coder's authorization endpoint:

   https://coder.example.com/oauth2/authorize?
     client_id=your-client-id&
     response_type=code&
     redirect_uri=https://yourapp.example.com/callback&
     state=random-string
   

2. Token Exchange: Exchange the authorization code for an access token.

   Option A: HTTP Basic authentication (client_secret_basic, recommended)

   curl -X POST \
     -u "$CLIENT_ID:$CLIENT_SECRET" \
     -H "Content-Type: application/x-www-form-urlencoded" \
     -d "grant_type=authorization_code" \
     -d "code=$AUTH_CODE" \
     -d "redirect_uri=https://yourapp.example.com/callback" \
     "$CODER_URL/oauth2/tokens"
   

   Option B: Form parameters (client_secret_post)

   curl -X POST \
     -H "Content-Type: application/x-www-form-urlencoded" \
     -d "grant_type=authorization_code" \
     -d "code=$AUTH_CODE" \
     -d "client_id=$CLIENT_ID" \
     -d "client_secret=$CLIENT_SECRET" \
     -d "redirect_uri=https://yourapp.example.com/callback" \
     "$CODER_URL/oauth2/tokens"
   

3. API Access: Use the access token to call Coder's API:

   curl -H "Authorization: Bearer $ACCESS_TOKEN" \
     "$CODER_URL/api/v2/users/me"
   

Note

The PKCE flow below is the required integration path. The example above is shown for reference but omits the mandatory code_challenge parameter. See PKCE Flow for the complete flow.

PKCE Flow (Required)

PKCE is required for all OAuth2 authorization code flows. Coder enforces PKCE in compliance with the OAuth 2.1 specification. Both public and confidential clients must include PKCE parameters:

1. Generate a code verifier and challenge:

   CODE_VERIFIER=$(openssl rand -base64 96 | tr -d "=+/" | cut -c1-128)
   CODE_CHALLENGE=$(echo -n $CODE_VERIFIER | openssl dgst -sha256 -binary | base64 | tr -d "=+/" | cut -c1-43)
   

2. Include PKCE parameters in the authorization request:

   https://coder.example.com/oauth2/authorize?
     client_id=your-client-id&
     response_type=code&
     code_challenge=$CODE_CHALLENGE&
     code_challenge_method=S256&
     redirect_uri=https://yourapp.example.com/callback
   

3. Include the code verifier in the token exchange (see Client Authentication Methods):

   curl -X POST \
     -u "$CLIENT_ID:$CLIENT_SECRET" \
     -H "Content-Type: application/x-www-form-urlencoded" \
     -d "grant_type=authorization_code" \
     -d "code=$AUTH_CODE" \
     -d "code_verifier=$CODE_VERIFIER" \
     -d "redirect_uri=https://yourapp.example.com/callback" \
     "$CODER_URL/oauth2/tokens"
   

Discovery Endpoints

Coder provides OAuth2 discovery endpoints for programmatic integration:

• Authorization Server Metadata: GET /.well-known/oauth-authorization-server
• Protected Resource Metadata: GET /.well-known/oauth-protected-resource

These endpoints return server capabilities and endpoint URLs according to RFC 8414 and RFC 9728.

Token Management

Refresh Tokens

Refresh an expired access token.

Option A: HTTP Basic authentication (client_secret_basic)

curl -X POST \
  -u "$CLIENT_ID:$CLIENT_SECRET" \
  -H "Content-Type: application/x-www-form-urlencoded" \
  -d "grant_type=refresh_token" \
  -d "refresh_token=$REFRESH_TOKEN" \
  "$CODER_URL/oauth2/tokens"

Option B: Form parameters (client_secret_post)

curl -X POST \
  -H "Content-Type: application/x-www-form-urlencoded" \
  -d "grant_type=refresh_token" \
  -d "refresh_token=$REFRESH_TOKEN" \
  -d "client_id=$CLIENT_ID" \
  -d "client_secret=$CLIENT_SECRET" \
  "$CODER_URL/oauth2/tokens"

Revoke Access

Revoke all tokens for an application:

curl -X DELETE \
  -H "Authorization: Bearer $CODER_SESSION_TOKEN" \
  "$CODER_URL/oauth2/tokens?client_id=$CLIENT_ID"

Testing and Development

Coder provides comprehensive test scripts for OAuth2 development:

# Navigate to the OAuth2 test scripts
cd scripts/oauth2/

# Run the full automated test suite
./test-mcp-oauth2.sh

# Create a test application for manual testing
eval $(./setup-test-app.sh)

# Run an interactive browser-based test
./test-manual-flow.sh

# Clean up when done
./cleanup-test-app.sh

For more details on testing, see the OAuth2 test scripts README.

Common Issues

"OAuth2 experiment not enabled"

Add oauth2 to your experiment flags: coder server --experiments oauth2

"Invalid redirect_uri"

Ensure the redirect URI in your request exactly matches the one registered for your application.

"PKCE verification failed"

Verify that the code_verifier used in the token request matches the one used to generate the code_challenge.

Security Considerations

• Use HTTPS: Always use HTTPS in production to protect tokens in transit
• Implement PKCE: PKCE is mandatory for all authorization code clients (public and confidential)
• Validate redirect URLs: Only register trusted redirect URIs for your applications
• Rotate secrets: Periodically rotate client secrets using the management API

Limitations

As an experimental feature, the current implementation has limitations:

• No scope system - all tokens have full API access
• No client credentials grant support
• Implicit grant (response_type=token) is not supported; OAuth 2.1 deprecated this flow due to token leakage risks, and requests return unsupported_response_type
• Limited to opaque access tokens (no JWT support)

Standards Compliance

This implementation follows established OAuth2 standards including RFC 6749 (OAuth2 core), RFC 7636 (PKCE), and the OAuth 2.1 draft. Coder enforces OAuth 2.1 requirements including mandatory PKCE for all authorization code grants, exact redirect URI string matching, rejection of the implicit grant, and CSRF protections on consent pages.

Next Steps

• Review the API Reference for complete endpoint documentation
• Check External Authentication for configuring Coder as an OAuth2 client
• See Security Best Practices for deployment security guidance

Feedback

This is an experimental feature under active development. Please report issues and feedback through GitHub Issues with the oauth2 label.