Authentication And Authorization In ASP.NET Core Web API With JSON Web Tokens

Introduction

Authentication is the process of validating user credentials and authorization is the process of checking privileges for a user to access specific modules in an application. In this article, we will see how to protect an ASP.NET Core Web API application by implementing JWT authentication. We will also see how to use authorization in ASP.NET Core to provide access to various functionality of the application. We will store user credentials in an SQL server database and we will use Entity framework and Identity framework for database operations.

JSON Web Token (JWT) is an open standard (RFC 7519) that defines a compact and self-contained way for securely transmitting information between parties as a JSON object. This information can be verified and trusted because it is digitally signed. JWTs can be signed using a secret (with the HMAC algorithm) or a public/private key pair using RSA or ECDSA.

In its compact form, JSON Web Tokens consist of three parts separated by dots (.), which are:

• Header
• Payload
• Signature

Therefore, a JWT typically looks like the following.

xxxx.yyyy.zzzz

Please refer to below link for more details about JSON Web Tokens.

https://jwt.io/introduction/

Create ASP.NET Core Web API using Visual Studio 2019

We can create an API application with ASP.NET Core Web API template.

We must install below libraries using NuGet package manager.

• Microsoft.EntityFrameworkCore.SqlServer
• Microsoft.EntityFrameworkCore.Tools
• Microsoft.AspNetCore.Identity.EntityFrameworkCore
• Microsoft.AspNetCore.Identity
• Microsoft.AspNetCore.Authentication.JwtBearer

We can modify the appsettings.json with below values.

appsettings.json

{  
  "Logging": {  
    "LogLevel": {  
      "Default": "Information",  
      "Microsoft": "Warning",  
      "Microsoft.Hosting.Lifetime": "Information"  
    }  
  },  
  "AllowedHosts": "*",  
  "ConnectionStrings": {  
    "ConnStr": "Data Source=(localdb)\\MSSQLLocalDB;Initial Catalog=SarathlalDB;Integrated Security=True;ApplicationIntent=ReadWrite;MultiSubnetFailover=False"  
  },  
  "JWT": {  
    "ValidAudience": "http://localhost:4200",  
    "ValidIssuer": "http://localhost:61955",  
    "Secret": "ByYM000OLlMQG6VVVp1OH7Xzyr7gHuw1qvUC5dcGt3SNM"  
  }  
}

We have added a database connection string and also added valid audience, valid issuer and secret key for JWT authentication in above settings file.

Create an “ApplicationUser” class inside a new folder “Authentication” which will inherit the IdentityUser class. IdentityUser class is a part of Microsoft Identity framework. We will create all the authentication related files inside the “Authentication” folder.

ApplicationUser.cs

using Microsoft.AspNetCore.Identity;  
  
namespace JWTAuthentication.Authentication  
{  
    public class ApplicationUser: IdentityUser  
    {  
    }  
}

We can create the “ApplicationDbContext” class and add below code.

ApplicationDbContext.cs

using Microsoft.AspNetCore.Identity.EntityFrameworkCore;  
using Microsoft.EntityFrameworkCore;  
  
namespace JWTAuthentication.Authentication  
{  
    public class ApplicationDbContext : IdentityDbContext<ApplicationUser>  
    {  
        public ApplicationDbContext(DbContextOptions<ApplicationDbContext> options) : base(options)  
        {  
  
        }  
        protected override void OnModelCreating(ModelBuilder builder)  
        {  
            base.OnModelCreating(builder);  
        }  
    }  
}

Create a static class “UserRoles” and add below values.

UserRoles.cs

namespace JWTAuthentication.Authentication  
{  
    public static class UserRoles  
    {  
        public const string Admin = "Admin";  
        public const string User = "User";  
    }  
}

We have added two constant values “Admin” and “User” as roles. You can add many roles as you wish.

Create class “RegisterModel” for new user registration.

RegisterModel.cs

using System.ComponentModel.DataAnnotations;  
  
namespace JWTAuthentication.Authentication  
{  
    public class RegisterModel  
    {  
        [Required(ErrorMessage = "User Name is required")]  
        public string Username { get; set; }  
  
        [EmailAddress]  
        [Required(ErrorMessage = "Email is required")]  
        public string Email { get; set; }  
  
        [Required(ErrorMessage = "Password is required")]  
        public string Password { get; set; }  
  
    }  
}

Create class “LoginModel” for user login.

LoginModel.cs

using System.ComponentModel.DataAnnotations;  
  
namespace JWTAuthentication.Authentication  
{  
    public class LoginModel  
    {  
        [Required(ErrorMessage = "User Name is required")]  
        public string Username { get; set; }  
  
        [Required(ErrorMessage = "Password is required")]  
        public string Password { get; set; }  
    }  
}

We can create a class “Response” for returning the response value after user registration and user login. It will also return error messages, if the request fails.

Response.cs

namespace JWTAuthentication.Authentication  
{  
    public class Response  
    {  
        public string Status { get; set; }  
        public string Message { get; set; }  
    }  
}

We can create an API controller “AuthenticateController” inside the “Controllers” folder and add below code.

AuthenticateController.cs

using JWTAuthentication.Authentication;  
using Microsoft.AspNetCore.Http;  
using Microsoft.AspNetCore.Identity;  
using Microsoft.AspNetCore.Mvc;  
using Microsoft.Extensions.Configuration;  
using Microsoft.IdentityModel.Tokens;  
using System;  
using System.Collections.Generic;  
using System.IdentityModel.Tokens.Jwt;  
using System.Security.Claims;  
using System.Text;  
using System.Threading.Tasks;  
  
namespace JWTAuthentication.Controllers  
{  
    [Route("api/[controller]")]  
    [ApiController]  
    public class AuthenticateController : ControllerBase  
    {  
        private readonly UserManager<ApplicationUser> userManager;  
        private readonly RoleManager<IdentityRole> roleManager;  
        private readonly IConfiguration _configuration;  
  
        public AuthenticateController(UserManager<ApplicationUser> userManager, RoleManager<IdentityRole> roleManager, IConfiguration configuration)  
        {  
            this.userManager = userManager;  
            this.roleManager = roleManager;  
            _configuration = configuration;  
        }  
  
        [HttpPost]  
        [Route("login")]  
        public async Task<IActionResult> Login([FromBody] LoginModel model)  
        {  
            var user = await userManager.FindByNameAsync(model.Username);  
            if (user != null && await userManager.CheckPasswordAsync(user, model.Password))  
            {  
                var userRoles = await userManager.GetRolesAsync(user);  
  
                var authClaims = new List<Claim>  
                {  
                    new Claim(ClaimTypes.Name, user.UserName),  
                    new Claim(JwtRegisteredClaimNames.Jti, Guid.NewGuid().ToString()),  
                };  
  
                foreach (var userRole in userRoles)  
                {  
                    authClaims.Add(new Claim(ClaimTypes.Role, userRole));  
                }  
  
                var authSigningKey = new SymmetricSecurityKey(Encoding.UTF8.GetBytes(_configuration["JWT:Secret"]));  
  
                var token = new JwtSecurityToken(  
                    issuer: _configuration["JWT:ValidIssuer"],  
                    audience: _configuration["JWT:ValidAudience"],  
                    expires: DateTime.Now.AddHours(3),  
                    claims: authClaims,  
                    signingCredentials: new SigningCredentials(authSigningKey, SecurityAlgorithms.HmacSha256)  
                    );  
  
                return Ok(new  
                {  
                    token = new JwtSecurityTokenHandler().WriteToken(token),  
                    expiration = token.ValidTo  
                });  
            }  
            return Unauthorized();  
        }  
  
        [HttpPost]  
        [Route("register")]  
        public async Task<IActionResult> Register([FromBody] RegisterModel model)  
        {  
            var userExists = await userManager.FindByNameAsync(model.Username);  
            if (userExists != null)  
                return StatusCode(StatusCodes.Status500InternalServerError, new Response { Status = "Error", Message = "User already exists!" });  
  
            ApplicationUser user = new ApplicationUser()  
            {  
                Email = model.Email,  
                SecurityStamp = Guid.NewGuid().ToString(),  
                UserName = model.Username  
            };  
            var result = await userManager.CreateAsync(user, model.Password);  
            if (!result.Succeeded)  
                return StatusCode(StatusCodes.Status500InternalServerError, new Response { Status = "Error", Message = "User creation failed! Please check user details and try again." });  
  
            return Ok(new Response { Status = "Success", Message = "User created successfully!" });  
        }  
  
        [HttpPost]  
        [Route("register-admin")]  
        public async Task<IActionResult> RegisterAdmin([FromBody] RegisterModel model)  
        {  
            var userExists = await userManager.FindByNameAsync(model.Username);  
            if (userExists != null)  
                return StatusCode(StatusCodes.Status500InternalServerError, new Response { Status = "Error", Message = "User already exists!" });  
  
            ApplicationUser user = new ApplicationUser()  
            {  
                Email = model.Email,  
                SecurityStamp = Guid.NewGuid().ToString(),  
                UserName = model.Username  
            };  
            var result = await userManager.CreateAsync(user, model.Password);  
            if (!result.Succeeded)  
                return StatusCode(StatusCodes.Status500InternalServerError, new Response { Status = "Error", Message = "User creation failed! Please check user details and try again." });  
  
            if (!await roleManager.RoleExistsAsync(UserRoles.Admin))  
                await roleManager.CreateAsync(new IdentityRole(UserRoles.Admin));  
            if (!await roleManager.RoleExistsAsync(UserRoles.User))  
                await roleManager.CreateAsync(new IdentityRole(UserRoles.User));  
  
            if (await roleManager.RoleExistsAsync(UserRoles.Admin))  
            {  
                await userManager.AddToRoleAsync(user, UserRoles.Admin);  
            }  
  
            return Ok(new Response { Status = "Success", Message = "User created successfully!" });  
        }  
    }  
}