OIDC Federation: Security Best Practices

TL;DR

Federating identity with a third party using OpenID Connect (OIDC) is common, but needs careful planning. This guide covers essential security steps to protect your users and data. Focus on strong authentication, proper configuration of scopes & claims, regular reviews, and monitoring.

1. Understand the Risks

Before you start, recognise what’s at stake:

• Data Exposure: Sharing user information with a third party increases risk if they have a breach.
• Phishing Attacks: Attackers might try to impersonate your service or the third party.
• Account Takeover: Weak authentication on either side can lead to compromised accounts.

2. Choose a Reputable Identity Provider (IdP)

The security of your federation relies heavily on the IdP. Look for:

• Compliance Certifications: SOC 2, ISO 27001 are good indicators.
• Security Audits: Ask about their audit history and penetration testing results.
• Multi-Factor Authentication (MFA): Ensure they offer robust MFA options.

3. Configure OIDC Properly

Correct configuration is vital. Here’s how:

1. Client Registration: Register your application with the IdP, specifying redirect URIs carefully. Only allow known and trusted redirect URLs.
2. Redirect URI Validation: Double-check that the redirect URIs are correct in both your application and the IdP configuration. A mismatch can lead to attacks.
3. Scopes: Request only the scopes you absolutely need. Avoid requesting openid, profile, and email unless essential. More scopes mean more data shared.

   # Example scope request (minimal)

   scope=openid profile email

4. Claims: Define the specific user attributes you require. Don’t ask for unnecessary information. Use standard claims where possible.

   # Example claim request (minimal)

   response_type=id_token token&scope=openid profile email&claims={ "sub": "required", "email": "required" }

5. Client Authentication: Use a strong client authentication method (e.g., Client Secret Post, Private Key JWT). Never embed secrets directly in client-side code.
6. Token Validation: Your application must validate the ID Token and Access Token received from the IdP.
   • Verify the signature using the IdP’s public key (available at their well-known endpoint).
   • Check the issuer (iss) claim.
   • Validate the audience (aud) claim.
   • Ensure the exp (expiration time) is valid.

4. Implement Strong Authentication

Protect your users:

• MFA: Encourage or enforce MFA for all users, especially administrators.
• Password Policies: If the IdP handles passwords, ensure they have strong password policies.
• Session Management: Implement appropriate session timeouts and idle session termination.

5. Secure Communication (HTTPS)

Always use HTTPS for all communication between your application, the IdP, and users.

6. Logging and Monitoring

Keep an eye on things:

• Log OIDC Events: Log authentication requests, token validation results, and any errors.
• Monitor for Anomalies: Look for unusual login patterns, failed authentications, or unexpected scope requests.
• Alerting: Set up alerts for critical events (e.g., repeated failed logins).

7. Regular Security Reviews

Don’t set it and forget it:

• Configuration Review: Regularly review your OIDC configuration to ensure it’s still appropriate.
• IdP Updates: Stay informed about updates from the IdP and apply security patches promptly.
• Penetration Testing: Conduct regular penetration testing of your application, including the OIDC integration.