How to start testing for writing methods for authorization and registration?

Question

Java

Hello. I sent a resume to Java Junior, in response they sent a test one:

1. Create api methods for registration and authorization (two methods).
2. Deploy them on any test server.
3. Provide a description of the methods (we will check through postman) and code (we will look at the approach).

I really don't know where to begin with this task.