Frequently asked questions and troubleshooting

This article contains frequently asked questions about Identity-Aware Proxy (IAP).

What apps can I secure with IAP?

IAP can be used with:

  • App Engine standard environment and App Engine flexible environment apps.
  • Compute Engine instances with HTTP(S) load balancing backend services.
  • Google Kubernetes Engine containers.
  • Cloud Run apps with HTTP(S) load balancing backend services.

Currently, IAP cannot be used with Cloud CDN.

Why is there a # at the end of my URL after signing in to my app?

In some browsers and under certain conditions, a # may be appended to the URL after authentication. This is normal and won't cause issues when logging in.

Why are my requests failing and returning a 405 Method Not Allowed status code?

This can be caused by not attaching cookies to your requests. By default, JavaScript methods don't attach cookies to requests.

The way you include cookies varies between request methods. For example, requests sent with an XMLHttpRequest object need the withCredentials property set to true, while requests sent with the Fetch API need the credentials option set to include or same-origin.

For information on handling errors that only occur after some time has passed, see Managing IAP sessions.

Why am I receiving an HTTP 401 Unauthorized status code instead of an HTTP 302 Redirect?

IAP responds with a 302 Redirect status code when a client is configured to handle redirects. To indicate that your client can handle redirects, ensure that HTTP Accept="text/html,*/*" is in the header of requests.

Why are POST requests not triggering redirects?

To trigger redirects, ensure that calls to IAP aren't POST requests. Browsers don't redirect as a response to POST requests. Because of this, IAP responds with a 401 Unauthorized status code instead of a 302 Redirect.

If you need IAP to serve POST requests, ensure that either the ID token or valid cookies are being passed in the header of the request.

Include the ID token in an Authorization: Bearer header to make an authenticated request to the IAP-secured resource. Obtain valid cookies by refreshing the session.

Can I use IAP if I have disabled the API?

Yes, access to resources secured with IAP works with the API disabled, but you won't be able to make changes to IAM permissions.

How can I restrict users with the Owner role from using IAP for TCP?

First, avoid using the Owner (roles/owner) role as much as possible. The Owner role grants wide permissions across Google Cloud. Assigning more granular roles and permissions can increase the security of your project. To learn more, see the IAM best practices.

If you cannot reduce usage of the Owner role, you can block IAP for TCP using Firewall rules.

What domain does IAP for TCP use?

IAP uses the following domains, which are owned by Google:

If you're connecting through a proxy server or firewall, make sure that they allow traffic to these domains, and that they don't block the use of WebSocket connections.

If you block traffic to these domains you will be unable to use IAP for TCP. You might receive one of several error messages.

If you are using gcloud, the error message might be

Error while connecting [[SSL: CERTIFICATE_VERIFY_FAILED] certificate verify failed

If you are using SSH from the browser the error message is

Cloud Identity-Aware Proxy Failed

There is no associated error code.

Why am I receiving the error Server Error?

If you receive the following error message, your firewall might be disallowing the IPs 130.211.0.0/22 and 35.191.0.0/16:

Error: Server Error
The server encountered a temporary error and could not complete your request.
Please try again in 30 seconds.

If the load balancer IPs 130.211.0.0/22 and 35.191.0.0/16 cannot reach your backend, your applications might not be accessible. For more information, see Setting up an external HTTPS load balancer.

If you are using IAP for TCP to connect to a specific VM, the VM must accept connections from addresses in the 35.235.240.0/20 range.

Why am I receiving intermittent internal server errors?

Receiving an error message with the format: An internal server error occurred while authorizing your request. Error code X indicates an internal failure. Internal errors with error codes 1 or 30 indicate backend failures. A low rate of these backend errors often indicate a transient issue. Clients should retry the request using exponential backoff.

Error codes

The following table lists common error codes and messages that return when configuring and using IAP.

Error code or message Description Troubleshooting
Error code 7 Your OAuth client ID or secret values are empty. Verify that your client ID and secret are correctly configured for your app by viewing the Credentials page. If your client ID and secret appear to be configured correctly, use the GET method to see the current state and PATCH method to reset the client ID and secret:
• Compute Engine API: GET, PATCH
• App Engine API: GET, PATCH
Error code 9 An OAuth redirect didn't complete. This is an internal error and has been logged for review.
Error code 9 (With path rewrite rules) An OAuth redirect didn't complete. Google Cloud Load Balancer path rewrite rules interferes with IAP's ability to successfully complete an OAuth flow. If you host multiple backends behind Google Cloud load balancer and use path rewrite rules, ensure that both the backends are using the same OAuth client IDs for IAP. You can change an OAuth client ID for a backend service by using the gcloud compute backend-services update command.
Error code 11 Your OAuth client ID is incorrectly configured. Verify that your client ID and secret are correctly configured for your app by viewing the Credentials page. If your client ID and secret appear to be configured correctly, use the GET method to see the current state and PATCH method to reset the client ID and secret:
• Compute Engine API: GET, PATCH
• App Engine API: GET, PATCH
Error code 13 Your OpenID Connect (OIDC) token is invalid. Ensure that the client ID configured for IAP isn't deleted by viewing the Credentials page.
Error code 51 Your browser does not support connection pooling. A current, up to date browser can handle connection pooling errors. Ensure that end users are using a current and up to date browser. For more information, see Restrict resource access to specific domains.
Error code 52 The host name provided does not match the SSL certificate on the server. The system administrator might need to update the SSL certificate. For more information see, Restrict resource access to specific domains.
Error code 53 The host name doesn't match the domains that are allowed by the IAP administrator. The administrator must update the list of allowed domains to include your host name. For more information see, Restrict resource access to specific domains.
Error code 429 Your project exceeds the per-minute threshold for requests. IAP projects are limited to a maximum of 360,000 requests per minute. If you encounter this error, reduce the volume of requests for your project. You can contact Google Cloud Support if you have additional questions.
Error code 4003 This might mean the instance isn't listening on the port you're trying to connect to or the firewall is closed. Either of those issues could also cause the start-up connectivity test to the VM instance to fail. Ensure that the listening process on the VM is running and listening on the correct port. Also, verify that your Google Cloud firewall is configured correctly and open on the port you're connecting to.
Error code 4010 A connection was established but closed by the destination instance. This usually indicates an issue on the instance or the program listening on the destination port. Reset the instance. If you are using SSH to connect, check the auth.log log for unexpected errors. The default location for the log file is /var/log/. If you can't access the logs using SSH, try using the serial console or detaching and reattaching the disk to a new VM to view the logs. Attach the logs when contacting customer support.
Error code 4033 Either you don't have permission to access the instance, the instance doesn't exist, or the instance is stopped. Ensure that you have the IAP-secured Tunnel User IAM role applied on the resource you're connecting to by viewing the Identity-Aware Proxy page.
Error code 4047 Either the instance doesn't exist, or the instance is stopped. Ensure that the VM is powered on and has completed its startup.

If you're unable to resolve your issue, please contact customer support with the description of your error and the response you get from a GET call to the API. You can remove your client secret from the response.