# 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:

```bash
coder server --experiments oauth2
```

Or set the environment variable:

```env
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` (web) or `myapp://callback` (native/desktop)
   - **Icon**: Optional icon URL

### Method 2: Management API

Create an application using the Coder API:

```bash
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:

```bash
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:

   ```url
   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)**

   ```bash
   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`)**

   ```bash
   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:

   ```bash
   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](#pkce-flow-required) 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:

   ```bash
   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:

   ```url
   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](#client-authentication-methods)):

   ```bash
   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](https://datatracker.ietf.org/doc/html/rfc8414) and [RFC 9728](https://datatracker.ietf.org/doc/html/rfc9728).

## Token Management

### Refresh Tokens

Refresh an expired access token.

**Option A: HTTP Basic authentication (`client_secret_basic`)**

```bash
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`)**

```bash
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:

```bash
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:

```bash
# 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](https://coder.com/docs/scripts/oauth2.md).

## 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.

### "Invalid Callback URL" on the consent page

If you see this error when authorizing, the registered callback URL uses a
blocked scheme (`javascript:`, `data:`, `file:`, or `ftp:`). Update the
application's callback URL to a valid scheme (see
[Callback URL schemes](#callback-url-schemes)).

### "PKCE verification failed"

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

## Callback URL schemes

Custom URI schemes (`myapp://`, `vscode://`, `jetbrains://`, etc.) are fully supported for native and desktop applications. The OS routes the redirect back to the registered application without requiring a running HTTP server.

The following schemes are blocked for security reasons: `javascript:`, `data:`, `file:`, `ftp:`.

## 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. Dangerous
  schemes (`javascript:`, `data:`, `file:`, `ftp:`) are blocked by the server,
  but custom URI schemes for native apps (`myapp://`) are permitted
- **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](https://datatracker.ietf.org/doc/html/rfc6749) (OAuth2 core),
[RFC 7636](https://datatracker.ietf.org/doc/html/rfc7636) (PKCE), and the
[OAuth 2.1 draft](https://datatracker.ietf.org/doc/html/draft-ietf-oauth-v2-1-12).
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](https://coder.com/docs/reference/api.md) for complete endpoint documentation
- Check [External Authentication](https://coder.com/docs/admin/external-auth.md) for configuring Coder as an OAuth2 client
- See [Security Best Practices](https://coder.com/docs/admin/security.md) for deployment security guidance

## Feedback

This is an experimental feature under active development. Please report issues and feedback through [GitHub Issues](https://github.com/coder/coder/issues) with the `oauth2` label.