A Zero-Downtime Guide to Rotating OIDC Client Secrets for AWS Application Load Balancers
In modern cloud architecture, securing user authentication is non-negotiable. Many organizations leverage an AWS Application Load Balancer (ALB) to handle authentication through an OpenID Connect (OIDC) compliant Identity Provider (IdP) like Okta, Azure AD, or Auth0. This setup is powerful, but it introduces a critical security task: managing and rotating the OIDC client secret.
Manually rotating these secrets is often a tedious and risky process. A single mistake can lead to application downtime, and failing to rotate them regularly exposes your system to unnecessary risk. Fortunately, you can build a robust, automated solution using native AWS services to handle this rotation with zero downtime.
This guide explores a powerful, event-driven architecture that automates the entire OIDC client secret rotation lifecycle, enhancing both your security posture and operational efficiency.
The Core Challenge: Avoiding Downtime During Rotation
The primary difficulty with rotating an ALB’s OIDC client secret is that an ALB listener rule can only be configured with one client secret at a time. If you simply generate a new secret and update the listener, any users with active sessions authenticated with the old secret may be abruptly logged out. The manual process often looks like this:
- Generate a new secret in your IdP.
- Quickly update the ALB listener rule with the new secret.
- Deactivate the old secret.
This sequence is fraught with peril. A delay between steps can cause login failures, and the instantaneous switchover provides no grace period for session transition, creating a poor user experience and potential service interruptions.
The Automated Solution: An Event-Driven Architecture
To solve this, we can design an automated workflow that intelligently manages the secret lifecycle. This architecture relies on a few key AWS services working in concert:
- AWS Secrets Manager: This service is the heart of the solution. It not only securely stores the OIDC client secret but also has built-in capabilities to manage a rotation schedule and lifecycle.
- AWS Lambda: A Lambda function serves as the central processing unit, containing the logic to communicate with your IdP, update Secrets Manager, and modify the ALB configuration.
- Amazon EventBridge: This acts as the scheduler, triggering the Lambda function based on a predefined rotation interval (e.g., every 90 days).
By combining these services, we create a hands-off system that ensures secrets are rotated on schedule without any manual intervention or service disruption.
The Step-by-Step Automated Rotation Process
The automated rotation process orchestrated by AWS Secrets Manager follows a well-defined, multi-stage flow to ensure a seamless transition from the old secret to the new one.
1. Initiation: The createSecret Step
The process begins when Amazon EventBridge triggers the rotation schedule. This invokes our primary Lambda function, which executes the first critical step:
- A new client secret is generated by making an API call to your Identity Provider (e.g., Okta, Azure AD). Your IdP must support multiple active client secrets for a single application to enable this zero-downtime pattern.
- The Lambda function then stores this newly generated secret in AWS Secrets Manager, marking it with the
AWSPENDINGlabel. At this point, the existing, active secret still has theAWSCURRENTlabel.
2. Activation: The setSecret Step
Immediately after the new secret is created and stored, the Lambda function proceeds to the activation stage. This is where the magic happens for preventing downtime.
- The Lambda function modifies the ALB’s listener rule to use the new client secret that was just placed in the
AWSPENDINGstage. - Once the ALB is successfully updated, the Lambda function promotes the new secret within Secrets Manager by changing its label from
AWSPENDINGtoAWSCURRENT. - Simultaneously, the secret that was previously in use is demoted to the
AWSPREVIOUSlabel.
At the end of this step, the new secret is live and handling all new authentication requests, while the old secret remains valid within the IdP for a grace period. This ensures that users with existing sessions are not impacted.
3. Validation: The testSecret Step
While optional, implementing a test step is a security best practice. A separate Lambda function can be invoked to perform a test authentication flow against the ALB. This verifies that the new AWSCURRENT secret is working correctly before the old one is permanently removed. If the test fails, you can roll back the changes or send an alert for manual review.
4. Finalization: The finishSecret Step
After a configurable grace period (e.g., a few hours or a day), Secrets Manager triggers the final stage of the rotation.
- The Lambda function is invoked one last time.
- It makes an API call to your IdP to permanently deactivate and delete the old client secret (the one labeled
AWSPREVIOUS). - This completes the rotation cycle, removing the old credential and ensuring only the new, active secret remains.
Key Benefits of Automating OIDC Secret Rotation
Adopting this automated approach provides significant advantages over manual processes:
- Enhanced Security: Regular, automated rotation dramatically reduces the risk of a compromised secret. By limiting the lifetime of each credential, you shrink the window of opportunity for attackers.
- Zero Downtime and Improved Reliability: The multi-stage process with a grace period ensures that the application remains fully available throughout the rotation, eliminating the risk of failed logins or interrupted user sessions.
- Operational Excellence: Automating this crucial but repetitive task frees up valuable engineering time and eliminates the potential for human error.
- Compliance and Auditing: This architecture provides a clear, auditable trail of when and how secrets were rotated, helping you meet strict compliance requirements.
By shifting from manual, high-risk secret management to an automated, event-driven workflow, you can build more secure, resilient, and efficient applications on AWS.
Source: https://aws.amazon.com/blogs/security/automate-oidc-client-secret-rotation-with-application-load-balancer/
