Why Do I Get a \'400 Bad Request Failed Precondition\' for Server-to-Server Authorization with Gmail REST API?

Gmail REST API: Troubleshooting "400 Bad Request Failed Precondition" for Server-to-Server Authentication

When attempting to send emails using the Gmail REST API via server-to-server communication, you may encounter a "400 Bad Request Failed Precondition" error. This error indicates that something is missing or incorrect with the request.

Problem:

You've configured the application client, downloaded credentials, and followed example programs for sending emails, but you continue to receive a "Bad Request" and "Precondition Failed" error when invoking the service.

Answer:

The issue may lie with incomplete or incorrect service account configuration. Ensure the following steps are followed precisely:

1. Create Google Credential:

   • Use the service account's client ID (ending in .apps.googleusercontent.com) as the serviceAccountClientID.
   • Use the service account user email (ending in @developer.gserviceaccount.com) as the serviceAccountUserEmail.
   • Set the service account scopes to include https://mail.google.com, https://www.googleapis.com/auth/gmail.compose, https://www.googleapis.com/auth/gmail.modify, and https://www.googleapis.com/auth/gmail.readonly.

2. Grant Domain-Wide Authorization:

   • In the Google Apps domain admin console, navigate to [Security] > [Advanced Settings].
   • Click on [Manage API Client Access].
   • Paste the client ID obtained in step 1 into the [Client Name] field.

By completing these steps, you can ensure that your service account has the necessary permissions and authority to access user data and send emails on their behalf.

The above is the detailed content of Why Do I Get a \'400 Bad Request Failed Precondition\' for Server-to-Server Authorization with Gmail REST API?. For more information, please follow other related articles on the PHP Chinese website!