AuthController.cs

using Microsoft.AspNetCore.Mvc;
using JWTAuth.API.Data;
using System.Threading.Tasks;
using JWTAuth.API.Models;
using JWTAuth.API.Dtos;

namespace JWTAuth.API.Controllers
{
    [Route("api/[controller]")]
    public class AuthController : Controller
    {
        private readonly IAuthRepository _repo;
        public AuthController(IAuthRepository repo)
        {
            _repo = repo;
        }

        [HttpPost("register")] //<host>/api/auth/register
        public async Task<IActionResult> Register([FromBody] UserForRegisterDto userForRegisterDto){ //Data Transfer Object containing username and password.
            // validate request
            if(!ModelState.IsValid)
                return BadRequest(ModelState);

            userForRegisterDto.Username = userForRegisterDto.Username.ToLower(); //Convert username to lower case before storing in database.

            if(await _repo.UserExists(userForRegisterDto.Username)) 
                return BadRequest("Username is already taken");

            var userToCreate = new User{
                Username = userForRegisterDto.Username
            };

            var createUser = await _repo.Register(userToCreate, userForRegisterDto.Password);

            return StatusCode(201);
        }
    }
}