This is a good answer to a similar question.
It basically says:
- Make a custom user class which implements
IUser - Define a custom user store which implements
public class UserStoreService
: IUserStore<CustomUser>, IUserPasswordStore<CustomUser> - wire everything up
Since the answer is pretty extensive I just provided the basic steps…
details are here: How to customize authentication to my own set of tables in asp.net web api 2?
This is also a very valuable content which also applies to web api:
Customizing ASP.NET Authentication with Identity by JumpStart
https://channel9.msdn.com/Series/Customizing-ASPNET-Authentication-with-Identity
HTH