Your code just broke—again—because an environment variable wasn’t set in the right place.
When you run behind Google Cloud’s Identity-Aware Proxy (IAP), environment variables can feel like a hidden trap. They’re essential for connecting to APIs, storing secrets, and defining runtime behavior, but when IAP steps in to protect your app, the way you handle and inject these variables changes. Misstep here, and you get endless 403s, failed connections, or weird authentication loops.
What is Identity-Aware Proxy Doing to Your Environment Variables?
IAP sits between the outside world and your application. It authenticates requests before they hit your code. This means any runtime environment—whether it’s App Engine, Cloud Run, or a Compute Engine instance—needs to be configured with the right environment variables so your app knows how to verify tokens, handle OAuth2 flows, and reach downstream APIs. The environment must contain service account credentials, audience (aud) values, and API endpoints in ways that survive across deployments and match the exact context where IAP enforces access.
The Right Way to Pass Variables Behind IAP
For Cloud Run, environment variables are defined at deployment. Forgetting one means redeploying. For App Engine, you set them in the app.yaml. For Compute Engine, you must load them from a secure source like Secret Manager or metadata server during startup. With IAP, you also need variables for verifying Google-signed JWTs—GOOGLE_CLOUD_PROJECT, IAP_AUDIENCE, and sometimes a base64 public key.
Your CI/CD pipeline must enforce these values. They should be stored securely, injected only in the runtime scope, and never hard-coded. When your service verifies IAP headers (X-Goog-Authenticated-User-Email, X-Goog-Authenticated-User-ID), those variables determine if the logic is valid or broken.