# OAuth2 Permission Scope Changes for Authenticated Users

When an application needs to request additional OAuth2 permissions (scopes) for an already authenticated user, requiring a complete re-login creates a poor user experience. This document outlines two effective approaches to handle permission scope changes without full re-authentication.

## 1. Using Refresh Tokens

Refresh tokens provide a way to obtain new access tokens without user interaction, potentially with updated scopes.

### How It Works

1. When the user initially authenticates, your application receives both an access token and a refresh token
2. When new permissions are needed, use the refresh token to request a new access token with expanded scopes
3. The OAuth provider issues a new access token with the updated permissions

### Implementation Example

/**
 * Updates OAuth2 scopes using a refresh token
 * @param {string} refreshToken - The user's refresh token
 * @param {string[]} newScopes - Array of all required scopes (existing + new)
 * @returns {Promise<object>} New token information
 */
async function updateScopesWithRefreshToken(refreshToken, newScopes) {
  try {
    // Using a generic OAuth2 client
    const response = await oauth2Client.refreshToken({
      refresh_token: refreshToken,
      scope: newScopes.join(' ')  // Typically space-delimited
    });
    
    // Store the new tokens
    const { access_token, refresh_token: new_refresh_token, expires_in } = response;
    
    // Update your token storage
    await storeTokens({
      accessToken: access_token,
      refreshToken: new_refresh_token || refreshToken, // Some providers don't return a new refresh token
      expiresAt: Date.now() + (expires_in * 1000),
      scope: newScopes.join(' ')
    });
    
    return response;
  } catch (error) {
    console.error('Failed to update scopes:', error);
    
    // If failed due to scope expansion limitations, fallback to visible authentication
    if (error.code === 'invalid_scope') {
      return requestVisibleAuthentication(newScopes);
    }
    
    throw error;
  }
}

### Provider-Specific Implementation (Google OAuth2)

const {google} = require('googleapis');
const oauth2Client = new google.auth.OAuth2(
  CLIENT_ID,
  CLIENT_SECRET,
  REDIRECT_URL
);

async function updateGoogleScopes(refreshToken, newScopes) {
  oauth2Client.setCredentials({
    refresh_token: refreshToken
  });
  
  try {
    // Request new token with updated scopes
    const response = await oauth2Client.refreshAccessToken({
      scope: newScopes.join(' ')
    });
    
    const tokens = response.credentials;
    // Store updated tokens
    return tokens;
  } catch (error) {
    console.error('Google OAuth scope update failed:', error);
    throw error;
  }
}

### Benefits and Limitations

**Benefits:**
- Completely invisible to the user
- No UI interruptions
- Fast token acquisition

**Limitations:**
- Not all OAuth providers support scope expansion via refresh tokens
- Some providers (like Google) only allow requesting the same or fewer scopes
- Security policies might restrict the use of refresh tokens for scope expansion

### Provider Support

| Provider | Supports Scope Expansion via Refresh | Notes |
|----------|--------------------------------------|-------|
| Google | No | Only same or fewer scopes |
| Microsoft/Azure AD | Limited | Depends on the consent type and permissions |
| Auth0 | Yes | Depends on configured settings |
| Okta | Limited | Depends on configured policies |
| GitHub | No | Requires new authorization |

## 2. Silent Re-authentication

Silent re-authentication leverages the user's existing session with the OAuth provider to obtain new tokens without user interaction, typically using hidden iframes.

### How It Works

1. Your application creates a hidden iframe
2. The iframe loads the OAuth provider's authorization URL with a special parameter (`prompt=none` or equivalent)
3. Since the user already has an active session with the provider, authentication happens silently
4. The provider redirects back to your application with new tokens
5. Your application captures the response via postMessage or URL monitoring

### Implementation Example

/**
 * Performs silent authentication to request additional scopes
 * @param {string[]} newScopes - Array of all required scopes
 * @returns {Promise<object>} New token information
 */
function silentAuthentication(newScopes) {
  return new Promise((resolve, reject) => {
    const iframe = document.createElement('iframe');
    iframe.style.display = 'none';
    
    // Generate random state value for security
    const state = generateRandomState();
    storeStateForValidation(state);
    
    // Add listener for message from auth page
    window.addEventListener('message', function handleMessage(event) {
      // Verify origin for security
      if (event.origin !== EXPECTED_ORIGIN) return;
      
      if (event.data.type === 'authorization_response') {
        window.removeEventListener('message', handleMessage);
        document.body.removeChild(iframe);
        
        // Validate state parameter
        if (event.data.response.state !== state) {
          reject(new Error('Invalid state parameter'));
          return;
        }
        
        resolve(event.data.response);
      }
    });
    
    // Construct authorization URL with prompt=none to prevent UI
    const authUrl = `${authorizationEndpoint}?` +
                    `client_id=${clientId}&` +
                    `redirect_uri=${redirectUri}&` +
                    `scope=${newScopes.join(' ')}&` +
                    `response_type=token&` +
                    `state=${state}&` +
                    `prompt=none`;  // Key parameter for silent auth
    
    iframe.src = authUrl;
    document.body.appendChild(iframe);
    
    // Set timeout in case of failure
    setTimeout(() => {
      if (document.body.contains(iframe)) {
        document.body.removeChild(iframe);
      }
      reject(new Error('Silent authentication timed out'));
    }, 10000);
  });
}

### Provider-Specific Example (Auth0)

function silentAuthWithAuth0(newScopes) {
  return new Promise((resolve, reject) => {
    const auth0Client = new auth0.WebAuth({
      domain: AUTH0_DOMAIN,
      clientID: AUTH0_CLIENT_ID,
      responseType: 'token id_token',
      redirectUri: window.location.origin + '/callback-silent.html',
      scope: newScopes.join(' ')
    });
    
    auth0Client.checkSession({
      prompt: 'none',
      scope: newScopes.join(' ')
    }, (err, authResult) => {
      if (err) {
        // If error.error === 'consent_required', user hasn't approved the new scopes
        reject(err);
        return;
      }
      
      resolve(authResult);
    });
  });
}

### Benefits and Limitations

**Benefits:**
- Invisible to the user when successful
- Works with most OAuth providers
- Can handle scope expansion better than refresh tokens

**Limitations:**
- Requires the user to have an active session with the OAuth provider
- If the user hasn't previously authorized the new scopes, this will typically fail
- Requires handling timeouts and errors gracefully
- Browser security settings might interfere with cross-domain iframe communication
- Must be performed in a browser context

### Handling Silent Authentication Failures

When silent authentication fails (usually because new permissions require user consent), fall back to visible authentication:

async function requestAdditionalScopes(newScopes) {
  try {
    // First try silent authentication
    const tokenResponse = await silentAuthentication(newScopes);
    return tokenResponse;
  } catch (error) {
    console.log('Silent authentication failed:', error);
    
    // If failed due to consent requirements, fall back to visible authentication
    if (error.error === 'consent_required' || error.error === 'interaction_required') {
      return visibleAuthentication(newScopes);
    }
    
    throw error;
  }
}

function visibleAuthentication(scopes) {
  // Redirect user to authorization page or open a popup
  // Implementation depends on your OAuth flow
}

## Choosing the Right Approach

| Consideration | Refresh Tokens | Silent Authentication |
|---------------|----------------|------------------------|
| Requires browser | No (can be done server-side) | Yes |
| Works for scope expansion | Provider-dependent | Yes, if user has pre-approved |
| User has active provider session | Not required | Required |
| Can be done in background | Yes | Yes |
| Fallback needed | Yes, if scope expansion not supported | Yes, if consent required |

## Best Practices

1. **Progressive Scopes**: Request minimal scopes initially, then incrementally request more as needed
2. **Graceful Fallbacks**: Always be prepared to fall back to visible authentication
3. **Clear User Communication**: If a visible auth is needed, explain to the user why additional permissions are required
4. **Security Considerations**:
- Always validate state parameters
- Use PKCE for public clients
- Securely store refresh tokens
5. **Monitoring**: Track success rates of silent authentication attempts to optimize the user experience

## Testing

Always test these approaches with each OAuth provider you support, as implementation details can vary significantly between providers. Test both the happy path (successful silent auth) and failure scenarios (consent required, session expired, etc.).