Awx 19.0.0 custom credential plugin

Hi,

I am trying to develop a credential plugin.
(login to api with an api key and retrieve an id that reurns username and password).

I am following the guide https://github.com/ansible/awx/blob/devel/docs/credentials/credential_plugins.md

Unfortunately this no longer works with Awx 19.0.0. Does any one know what the correct steps are to install a credential plugin in awx 19.0.0.

kind regards

Stefan