podnoms/server/Controllers/AuthController.cs

using System.Security.Claims;
using System.Threading.Tasks;
using Microsoft.AspNetCore.Identity;
using Microsoft.AspNetCore.Mvc;
using Microsoft.Extensions.Options;
using Newtonsoft.Json;
using PodNoms.Api.Models;
using PodNoms.Api.Models.ViewModels;
using PodNoms.Api.Services.Auth;
using PodNoms.Api.Utils;

namespace PodNoms.Api.Controllers {
    [Route("[controller]")]
    public class AuthController : Controller {
        private readonly UserManager<ApplicationUser> _userManager;
        private readonly IJwtFactory _jwtFactory;
        private readonly JwtIssuerOptions _jwtOptions;

        public AuthController(UserManager<ApplicationUser> userManager, IJwtFactory jwtFactory, IOptions<JwtIssuerOptions> jwtOptions) {
            _userManager = userManager;
            _jwtFactory = jwtFactory;
            _jwtOptions = jwtOptions.Value;
        }

        // POST api/auth/login
        [HttpPost("login")]
        public async Task<IActionResult> Post([FromBody]CredentialsViewModel credentials) {
            if (!ModelState.IsValid) {
                return BadRequest(ModelState);
            }

            var identity = await GetClaimsIdentity(credentials.UserName, credentials.Password);
            if (identity == null) {
                return BadRequest(Errors.AddErrorToModelState("login_failure", "Invalid username or password.", ModelState));
            }

            var jwt = await Tokens.GenerateJwt(identity, _jwtFactory, credentials.UserName, _jwtOptions, 
                new JsonSerializerSettings { Formatting = Formatting.Indented });
            return new OkObjectResult(jwt);
        }

        private async Task<ClaimsIdentity> GetClaimsIdentity(string userName, string password) {
            if (string.IsNullOrEmpty(userName) || string.IsNullOrEmpty(password))
                return await Task.FromResult<ClaimsIdentity>(null);

            // get the user to verifty
            var userToVerify = await _userManager.FindByNameAsync(userName);

            if (userToVerify == null) return await Task.FromResult<ClaimsIdentity>(null);

            // check the credentials
            if (await _userManager.CheckPasswordAsync(userToVerify, password)) {
                return await Task.FromResult(_jwtFactory.GenerateClaimsIdentity(userName, userToVerify.Id));
            }

            // Credentials are invalid, or account doesn't exist
            return await Task.FromResult<ClaimsIdentity>(null);
        }
    }
}