Just a quick addition here. I managed to get this working on 3.11. It's really quite simple actually. Just go to the GitHub page where the plugin is located and download the branch titled VERSION3.
Here is a direct link to the page which is also available on the plugin page here on Moodle.org. --> https://github.com/catalyst/moodle-auth_enrolkey
Don't forget to change the title of the package that is installed to --> enrolkey
It will update the current version you have installed if you've installed from the Plugins directory here on Moodle.
Cheers
Jason
Here is a direct link to the page which is also available on the plugin page here on Moodle.org. --> https://github.com/catalyst/moodle-auth_enrolkey
Don't forget to change the title of the package that is installed to --> enrolkey
It will update the current version you have installed if you've installed from the Plugins directory here on Moodle.
Cheers
Jason