How to implement REST API with generic account?

Question

API

I can't figure out how to optimally organize the interaction of two APIs:
The first API stores password accounts, the second is a project. To enter the project - you need to enter the login-password from the universal account (the first API). And so for all future projects.
The question is not in the specific implementation, but in the idea.
PS SSO - not what you need. The goal is not single sign-on, but a single account.

Answer 1

You make a single authorization center in any convenient form (RESTFUL), in projects you create authorization functions using a single center. It is better to register an account not in projects, but on the main page of this center. All TM services use this approach (Habr, Megamind, Giktimes, Toaster), see how they implement it.