The link you provided is a legacy SSO offering that only worked with Adobe Analytics. This offering has been deprecated in favor of the Marketing Cloud SSO. You can learn more about the various identity types here. If you decided federated IDs are preferable for your organization, you can read through some of our SSO documentation here. Please let me know if you have additional questions after reviewing those links.
I don't believe it is possible to setup your own custom authentication into any Adobe solution. If you are looking for SSO capabilities, the Adobe Marketing Cloud has an SSO offering. If you'd like more information about that, I can see if I can pull an expert into the thread.