It is possible to create a quick login for your helpdesk via GitHub. To activate the quick login you need to enable OAuth for GitHub.
Visit https://github.com/settings/applications/new and enter the app settings. As callback URL enter "https://zammad_host/auth/github/callback" where zammad_host has to be replaced with your Zammad FQDN
Enter the "APP ID" and the "APP SECRET" from the GitHub OAUTH Applications Dashboard
After you configured the GitHub credentials and activated the login method, you should see a new icon on the login page.
If you click on the icon you will be redirected to GitHub and see something similar to this:
When you grant the access you will be redirected to your Zammad instance and logged in as a customer.
Now you can link accounts via "Avatar -> Profile -> Link Accounts" or login via Zammad login page.