Well then.. the OAuth2 question I even considered but I prefer to keep the minimum of external tools..
Based on your second option would be: Remove the password field from my system and when performing the user registration do an insert/update in the 2 databases (fusio and software) and authentication I perform in fusio...
I will study the tool a little more and do some tests.
Thanks for the reply, and by the way..great work.
If I manage to integrate the tool into my software, I will make a donation to the project.
Compliments..