I am very much in need of Auth0 authentication. This should allow for SSO capabilities both across installations of Woltlab and between other products. I would write this myself, but I have just started with PHP and working with a third-party product adds a level of complexity I'm not ready for. Plus, if I were to write and release this plugin, it would not see a German release until someone takes the time to translate it, which is the opposite of the status-quo of most WoltLab plugins.
The documentation for Auth0 with PHP is located here: 01-login
Auth0 is a free product, so setting up a testing environment for development of the plugin will not be an issue. Plus, the documentation is not that log, so I assume it's not a very involved process.