JWT on .NET Core 2.0

Here is a full working minimal sample with a controller. I hope you can check it using Postman or JavaScript call.

1. appsettings.json, appsettings.Development.json. Add a section. Note, Key should be rather long and Issuer is an address of the service:

   ...
   ,"Tokens": {
       "Key": "Rather_very_long_key",
       "Issuer": "http://localhost:56268/"
   }
   ...
   

   !!! In real project, don’t keep Key in appsettings.json file. It should be kept in Environment variable and take it like this:

   Environment.GetEnvironmentVariable("JWT_KEY");
   

UPDATE: Seeing how .net core settings work, you don’t need to take it exactly from Environment. You may use setting. However,instead we may write this variable to environment variables in production, then our code will prefer environment variables instead of configuration.

2. AuthRequest.cs : Dto keeping values for passing login and password:

   public class AuthRequest
   {
       public string UserName { get; set; }
       public string Password { get; set; }
   }
   

3. Startup.cs in Configure() method BEFORE app.UseMvc() :

   app.UseAuthentication();
   

4. Startup.cs in ConfigureServices() :

   services.AddAuthentication()
       .AddJwtBearer(cfg =>
       {
           cfg.RequireHttpsMetadata = false;
           cfg.SaveToken = true;
   
           cfg.TokenValidationParameters = new TokenValidationParameters()
           {
               ValidIssuer = Configuration["Tokens:Issuer"],
               ValidAudience = Configuration["Tokens:Issuer"],
               IssuerSigningKey = new SymmetricSecurityKey(Encoding.UTF8.GetBytes(Configuration["Tokens:Key"]))
           };
   
       });
   

5. Add a controller:

       [Route("api/[controller]")]
       public class TokenController : Controller
       {
           private readonly IConfiguration _config;
           private readonly IUserManager _userManager;
   
           public TokenController(IConfiguration configuration, IUserManager userManager)
           {
               _config = configuration;
               _userManager = userManager;
           }
   
           [HttpPost("")]
           [AllowAnonymous]
           public IActionResult Login([FromBody] AuthRequest authUserRequest)
           {
               var user = _userManager.FindByEmail(model.UserName);
   
               if (user != null)
               {
                   var checkPwd = _signInManager.CheckPasswordSignIn(user, model.authUserRequest);
                   if (checkPwd)
                   {
                       var claims = new[]
                       {
                           new Claim(JwtRegisteredClaimNames.Sub, user.UserName),
                           new Claim(JwtRegisteredClaimNames.Jti, user.Id.ToString()),
                       };
   
                       var key = new SymmetricSecurityKey(Encoding.UTF8.GetBytes(_config["Tokens:Key"]));
                       var creds = new SigningCredentials(key, SecurityAlgorithms.HmacSha256);
   
                       var token = new JwtSecurityToken(_config["Tokens:Issuer"],
                       _config["Tokens:Issuer"],
                       claims,
                       expires: DateTime.Now.AddMinutes(30),
                       signingCredentials: creds);
   
                       return Ok(new { token = new JwtSecurityTokenHandler().WriteToken(token) });
                   }
               }
   
               return BadRequest("Could not create token");
           }}
   

That’s all folks! Cheers!

UPDATE: People ask how get Current User. Todo:

1. In Startup.cs in ConfigureServices() add

   services.AddSingleton<IHttpContextAccessor, HttpContextAccessor>();
   

2. In a controller add to constructor:

   private readonly int _currentUser;
   public MyController(IHttpContextAccessor httpContextAccessor)
   {
      _currentUser = httpContextAccessor.CurrentUser();
   }
   

3. Add somewhere an extension and use it in your Controller (using ….)

   public static class IHttpContextAccessorExtension
   {
       public static int CurrentUser(this IHttpContextAccessor httpContextAccessor)
       {
           var stringId = httpContextAccessor?.HttpContext?.User?.FindFirst(JwtRegisteredClaimNames.Jti)?.Value;
           int.TryParse(stringId ?? "0", out int userId);
   
           return userId;
       }
   }