Jenkins Job Fails with "Access Denied" for GitHub Pull Requests Despite Correct Permissions

A rare issue with Jenkins occurs when a job fails with an Access Denied error for GitHub pull requests, despite the correct permissions being set in both Jenkins and GitHub.

This can be caused by several issues related to authentication, permissions, or misconfigurations in either system.

The first thing to check is the GitHub webhook configuration.

When using GitHub integration with Jenkins, it’s crucial that the webhook URL is correctly configured to trigger Jenkins jobs when pull requests are created or updated.

Ensure that the webhook is set to deliver the appropriate events, such as Pull Request or Push, and that the webhook URL matches the correct endpoint on your Jenkins server.

If the webhook is misconfigured or not triggering, the Jenkins job will not run, and you may see an Access Denied error.

Another potential cause is the GitHub personal access token (PAT) or OAuth token used for authentication.

If the token has expired, been revoked, or lacks the required permissions, Jenkins will be unable to authenticate the user for the pull request, resulting in access issues.

Go to GitHub and check the status of the token, ensuring that it has the necessary permissions to read pull requests and trigger Jenkins jobs.

In Jenkins, verify that the token is properly configured in the GitHub plugin settings under Manage Jenkins > Configure System > GitHub section.

If you're using SSH keys for authentication, ensure that the correct SSH key is being used and that it is authorized in both Jenkins and GitHub.

Additionally, check the Jenkins job's configuration.

In the job settings, under Build Triggers, make sure that the correct GitHub trigger is selected to listen for pull request events.

Without the correct trigger, the job will not be able to process pull request events, leading to errors.

If you're using GitHub organization webhooks, ensure that the organization is correctly configured and that Jenkins has the necessary permissions to access the repositories under the organization.

Lastly, check for any firewall or proxy issues that might be blocking Jenkins from accessing GitHub or vice versa.

Network restrictions can sometimes interfere with authentication and webhook delivery.

If necessary, try testing the webhook or token using external tools to ensure they are working as expected.

If the issue persists, consider reconfiguring the Jenkins job from scratch, ensuring that all authentication and permissions are correctly set up.