REST(ful) API issues can all be resolved with one addition:
Adding actions to it!
POST api/registration / api/signup? All of this sucks. Posting or putting on api/user? Also doesn‘t feel right.
POST to api/user:signup
Boom! Full REST for entities + actions with custom requests and responses for actions!
How do I make a restful filter call? GET request params are not enough…
You POST to api/user:search, boom!
(I prefer to use the description RESTful API, instead of REST API -everyone fails to implement pure REST anyways, and it‘s unnecessarily limited.)
What is the problem with posting to /user/signup that posting to /user:signup solves?
You might not want a dedicated „Signup“ entity in your model and db.
you would POST to /users
what's the confusion? you're creating a new user entity in the users collection.