Authentication and authorization are essential components of any web application, ensuring the security and proper access control for users. In NET Core, these concepts play a crucial role in protecting resources and determining user permissions.   Authentication in NET Core Authentication is the process of verifying the identity of a user, ensuring they are who they claim to be. This is typically done by presenting credentials, such as a username and password, and validating them against a trusted source, such as a database or an external authentication provider. Once authenticated, the user is assigned an identity, which is then used for subsequent authorization checks.   Authentication in NET Core Authentication in NET Core revolves around the concept of authentication schemes. An authentication scheme represents a specific method or protocol used to authenticate users. NET Core supports various authentication schemes out of the box, including cookie authentication, JWT bearer authentication, and external authentication providers like OAuth and OpenID Connect.   Understanding Authentication Schemes Authentication schemes are registered in the application’s startup class using the AddAuthentication method. This method allows you to specify one or more authentication schemes and their respective options. For example, to enable cookie authentication, you can use the AddCookie   services.AddAuthentication(CookieAuthenticationDefaults.AuthenticationScheme) .AddCookie(options => { // Configure CookieAuthenticationDefaults options });   Configuring Cookie Authentication To configure cookie authentication, you need to specify the authentication scheme as CookieAuthenticationDefaults.AuthenticationScheme and provide the necessary options, such as the cookie name, login path, and authentication endpoint. Here's an example: services.AddAuthentication(CookieAuthenticationDefaults.AuthenticationScheme) .AddCookie(options => { options.Cookie.Name = "MyCookie"; options.LoginPath = "/Admin/Login"; }); In this example, the cookie authentication middleware is configured to use the scheme named “MyCookie” and redirect users to the “/Admin/Login” page if they try to access a protected resource without being authenticated. The options object allows you to customize various aspects of cookie authentication, such as cookie expiration and sliding expiration.   Implementing Claim-Based Authentication A claim represents a piece of information about the user, such as their name, email address, or role. By using claims, you can easily extend the user’s identity with additional data and make authorization decisions based on these claims. In NET Core, claim-based authentication is implemented using the ClaimsIdentity and ClaimsPrincipal classes. The ClaimsIdentity represents a collection of claims associated with a user, while the ClaimsPrincipal represents the user's identity as a whole. When a user is authenticated, their claims are stored in a ClaimsPrincipal, which is then attached to the current request's HttpContext.User property. To implement claim-based authentication, you need to create and populate a ClaimsIdentity object with the relevant claims. This can be done during the authentication process, typically in a custom authentication handler. Here's an example of how to create a ClaimsIdentity with a username claim:   var claims = new List<Claim> { new Claim(ClaimTypes.Name, "Himanshu") }; var identity = new ClaimsIdentity(claims, "MyAuthenticationScheme"); var principal = new ClaimsPrincipal(identity); await HttpContext.SignInAsync(principal);   External Authentication Providers External authentication allows users to sign in to your application using their existing accounts from popular platforms like Google, Facebook, Twitter, and Microsoft.  To enable external authentication, you need to configure the desired authentication provider and register it in your application’s startup class.   services.AddAuthentication() .AddGoogle(options => { options.ClientId = "YOUR_GOOGLE_CLIENT_ID"; options.ClientSecret = "YOUR_GOOGLE_CLIENT_SECRET"; });   Securing APIs with JWT Bearer Authentication .NET Core provides built-in support for securing APIs using JSON Web Tokens (JWT) and the JWT bearer authentication scheme. JWTs are self-contained tokens that contain information about the user and their permissions. By validating the integrity and authenticity of a JWT, you can trust the claims it contains and authenticate API requests. To enable JWT bearer authentication, you need to configure the authentication scheme and provide the necessary options, such as the token validation parameters and the issuer signing key. Here’s an example of configuring JWT bearer authentication: services.AddAuthentication(JwtBearerDefaults.AuthenticationScheme) .AddJwtBearer(options => { options.TokenValidationParameters = new TokenValidationParameters { ValidateIssuer = true, ValidateAudience = true, ValidateIssuerSigningKey = true, ValidIssuer = "YOUR_ISSUER", ValidAudience = "YOUR_AUDIENCE", IssuerSigningKey = new SymmetricSecurityKey(Encoding.UTF8.GetBytes("YOUR_SIGNING_KEY")) }; }); In this example, the AddJwtBearer extension method is used to configure JWT bearer authentication. The TokenValidationParameters object is set with the necessary validation rules, such as validating the issuer, audience, and the issuer's signing key. You need to replace the placeholder values with your own values specific to your JWT setup. With JWT bearer authentication enabled, API endpoints can be protected by applying the [Authorize] attribute to the corresponding controller or action. This ensures that only requests with valid and authenticated JWTs are allowed access to the protected resources.   Maintain secure Authorization Authorization in NET Core is primarily controlled through the use of the [Authorize] attribute. This attribute can be applied at the controller or action level to restrict access to specific components of your application. By default, the [Authorize] attribute allows only authenticated users to access the protected resource. The Role of Authorize Attribute :  For example, you can use the [Authorize(Roles = "Admin")] attribute to restrict access to administrators only. This ensures that only users with the "Admin" role can access the protected resource. Restricting Access with Policies : While the [Authorize] attribute provides a simple way to restrict access, ASP.NET Core also supports more advanced authorization policies. Authorization policies allow you to define fine-grained rules for determining whether a user is authorized to perform a specific action. To use authorization policies, you need to define them in your application’s startup class using the AddAuthorization method. Here's an example:   services.AddAuthorization(options => { options.AddPolicy("AdminOnly", policy => { policy.RequireRole("Admin"); }); }); Rrole-based authorization can be implemented using the built-in role-based authentication system or by integrating with an external identity provider, such as Active Directory or Azure AD.   Implementing Two-Factor Authentication Two-factor authentication (2FA) adds an extra layer of security to the authentication process by requiring users to provide additional verification, typically in the form of a one-time password or a biometric factor. Implementing 2FA can significantly reduce the risk of unauthorized access, especially for sensitive applications or those handling confidential information.   To implement two-factor authentication, you need to configure the desired authentication providers, such as SMS, email, or authenticator apps, and register them in your application’s startup class. You also need to configure the necessary options, such as the message templates or the issuer signing key. By enabling two-factor authentication, you provide an additional layer of security that can help protect user accounts from unauthorized access, even if their credentials are compromised.   Protecting Against Common Security Vulnerabilities When implementing authentication and authorization in your application, it’s crucial to be aware of common security vulnerabilities and take appropriate measures to prevent them. By understanding these vulnerabilities and following security best practices, you can ensure the integrity and confidentiality of user data. Some common security vulnerabilities to consider when implementing authentication and authorization include: Cross-Site Scripting (XSS): Protect against XSS attacks by properly encoding user input and validating data before rendering it in HTML or JavaScript. Cross-Site Request Forgery (CSRF): Implement CSRF protection mechanisms, such as anti-forgery tokens, to prevent attackers from executing unauthorized actions on behalf of authenticated users. Brute-Force Attacks: Implement account lockout policies and rate limiting to protect against brute-force attacks that attempt to guess user credentials. Session Management: Use secure session management techniques, such as session timeouts, secure cookie attributes, and session regeneration, to prevent session hijacking or session fixation attacks. Password Storage: Store passwords securely by using strong hashing algorithms, salting, and iteration counts to protect against password cracking attempts. By addressing these vulnerabilities and following security best practices, you can minimize the risk of unauthorized access, data breaches, and other security incidents.   Conclusion: Authentication and authorization are critical components of building secure and robust web applications in .Net Core. By understanding the concepts and leveraging the powerful features provided by. NET Core, developers can implement robust security measures to protect their applications and ensure that users access resources securely and efficiently.

What is Authorization?  Authorization verifies whether a user has permission to use specific applications or services. While authentication and authorization are distinct processes, authentication must precede authorization, ensuring the user's identity is confirmed before determining their access rights.    When logging into a system, a user must provide credentials like a username and password to authenticate. Next, the authorization process grants rights. For example, an administrative user can create a document library to add, edit, and delete documents, while a non-administrative user can only read documents in the library.  Types of Authorization:  Simple Authorization  Role-Based Authorization  Claim-Based Authorization  Policy-Based Authorization  I have implemented an example of role-based authorization in .NET. Step 1: Create one new MVC Web Application with the Authentication type “Individual Account”.  Step 2: Register Identity with DefaultTokenProvider in the program.cs file. builder.Services.AddIdentity<IdentityUser, IdentityRole>(options => options.SignIn.RequireConfirmedAccount = false) .AddEntityFrameworkStores<ApplicationDbContext>() .AddDefaultTokenProviders(); For better understanding, I have added one page to add a new role.  Create a new method in the controller and add the following code. [HttpGet] public IActionResult Admin() { return View(); } Create a new model Role.cs.   namespace Authorization.Models { public class Role { public string RoleName { get; set; } } } Create html page for add role.  @model Role @{ ViewData["Title"] = "Admin"; } <h1>Admin</h1> <div class="row"> <div class="col-md-12"> <form method="post" action="@Url.Action("Admin","Home")"> <div class="form-group"> <label>Role Name</label> <input type="text" class="form-control" style="width:30%;" asp-for="RoleName" placeholder="Role name" required> </div> <br /> <button class="btn btn-success" type="submit">Add</button> </form> </div> </div> I have created a simple page, You can modify the page as per your requirements.  Add a new method in the controller and add the following code. And declare RoleManager<IdentityRole> and inject in the constructor. private readonly RoleManager<IdentityRole> _roleManager; public HomeController(RoleManager<IdentityRole> roleManager) { _roleManager = roleManager; } [HttpPost] public async Task<IActionResult> Admin(Role role) { var result = _roleManager.RoleExistsAsync(role.RoleName).Result; if (!result) { await _roleManager.CreateAsync(new IdentityRole(role.RoleName)); } return RedirectToAction("Admin"); } Set a new tab in _Layout.cshtml file to redirect to the Add role page.  <li class="nav-item"> <a class="nav-link text-dark" asp-area="" asp-controller="Home" asp-action="Admin">Add new role</a> </li> Run the project and you will see the output. Here, You can add a new role.  Add a new field in register.cshtml using the following code to assign a role to the user.  <div class="form-floating mb-3"> <select asp-for="Input.Role" class="form-control" aria-required="true"> <option value="">Select role</option> @foreach (var item in Model.RoleList) { <option value="@item.Name">@item.Name</option> } </select> <span asp-validation-for="Input.ConfirmPassword" class="text-danger"></span> </div> To get the list of roles you can add the following code in your register.cshtml.cs file. And Add  RoleList = _roleManager.Roles in OnPostAsync method also. public IQueryable<IdentityRole> RoleList { get; set; } public async Task OnGetAsync(string returnUrl = null) { ReturnUrl = returnUrl; RoleList = _roleManager.Roles; ExternalLogins = (await _signInManager.GetExternalAuthenticationSchemesAsync()).ToList(); } Run the project and see the output. Now, Assign the role to the user, and for that add the following code in OnPostAsync after the user is created. await _userManager.AddToRoleAsync(user, Input.Role); Full code of register.cshtml.cs file. using Microsoft.AspNetCore.Authentication; using Microsoft.AspNetCore.Identity; using Microsoft.AspNetCore.Mvc; using Microsoft.AspNetCore.Mvc.RazorPages; using Microsoft.AspNetCore.WebUtilities; using System.ComponentModel.DataAnnotations; using System.Text; namespace Authorization.Areas.Identity.Pages.Account { public class RegisterModel : PageModel { private readonly SignInManager<IdentityUser> _signInManager; private readonly UserManager<IdentityUser> _userManager; private readonly RoleManager<IdentityRole> _roleManager; private readonly IUserStore<IdentityUser> _userStore; private readonly IUserEmailStore<IdentityUser> _emailStore; private readonly ILogger<RegisterModel> _logger; //private readonly IEmailSender _emailSender; public RegisterModel( UserManager<IdentityUser> userManager, IUserStore<IdentityUser> userStore, SignInManager<IdentityUser> signInManager, ILogger<RegisterModel> logger, RoleManager<IdentityRole> roleManager ) { _userManager = userManager; _userStore = userStore; _emailStore = GetEmailStore(); _signInManager = signInManager; _roleManager = roleManager; _logger = logger; } [BindProperty] public InputModel Input { get; set; } public IQueryable<IdentityRole> RoleList { get; set; } public string ReturnUrl { get; set; } public IList<AuthenticationScheme> ExternalLogins { get; set; } public class InputModel { [Required] [EmailAddress] [Display(Name = "Email")] public string Email { get; set; } [Required] [Display(Name = "Role")] public string Role { get; set; } [Required] [StringLength(100, ErrorMessage = "The {0} must be at least {2} and at max {1} characters long.", MinimumLength = 6)] [DataType(DataType.Password)] [Display(Name = "Password")] public string Password { get; set; } [DataType(DataType.Password)] [Display(Name = "Confirm password")] [Compare("Password", ErrorMessage = "The password and confirmation password do not match.")] public string ConfirmPassword { get; set; } } public async Task OnGetAsync(string returnUrl = null) { ReturnUrl = returnUrl; RoleList = _roleManager.Roles; ExternalLogins = (await _signInManager.GetExternalAuthenticationSchemesAsync()).ToList(); } public async Task<IActionResult> OnPostAsync(string returnUrl = null) { returnUrl ??= Url.Content("~/"); RoleList = _roleManager.Roles; ExternalLogins = (await _signInManager.GetExternalAuthenticationSchemesAsync()).ToList(); if (ModelState.IsValid) { var user = CreateUser(); await _userStore.SetUserNameAsync(user, Input.Email, CancellationToken.None); await _emailStore.SetEmailAsync(user, Input.Email, CancellationToken.None); var result = await _userManager.CreateAsync(user, Input.Password); if (result.Succeeded) { _logger.LogInformation("User created a new account with password."); await _userManager.AddToRoleAsync(user, Input.Role); var userId = await _userManager.GetUserIdAsync(user); var code = await _userManager.GenerateEmailConfirmationTokenAsync(user); code = WebEncoders.Base64UrlEncode(Encoding.UTF8.GetBytes(code)); if (_userManager.Options.SignIn.RequireConfirmedAccount) { return RedirectToPage("RegisterConfirmation", new { email = Input.Email, returnUrl = returnUrl }); } else { await _signInManager.SignInAsync(user, isPersistent: false); return LocalRedirect(returnUrl); } } foreach (var error in result.Errors) { ModelState.AddModelError(string.Empty, error.Description); } } return Page(); } private IdentityUser CreateUser() { try { return Activator.CreateInstance<IdentityUser>(); } catch { throw new InvalidOperationException($"Can't create an instance of '{nameof(IdentityUser)}'. " + $"Ensure that '{nameof(IdentityUser)}' is not an abstract class and has a parameterless constructor, or alternatively " + $"override the register page in /Areas/Identity/Pages/Account/Register.cshtml"); } } private IUserEmailStore<IdentityUser> GetEmailStore() { if (!_userManager.SupportsUserEmail) { throw new NotSupportedException("The default UI requires a user store with email support."); } return (IUserEmailStore<IdentityUser>)_userStore; } } } Now, register one new user and assign a role to them. For example, I have created one user and assign “Admin” to them. I have added two new methods in the controller and added a default view for that.  [Authorize(Roles = "User")] public IActionResult UserRoleCheck() { return View(); } [Authorize(Roles = "Admin")] public IActionResult AdminRoleCheck() { return View(); } I have set the Authorize attribute with the role name on both authorization methods. Now, I am running the project and clicking on Admin Role, It will open the page of admin because the logged user role and method role both are the same.  If I click on User Role, It will give an Access denied error. Because logged user role and method role both are different. Here, I am using by default access denied page of identity. You can use custom page also, Just set this path to program.cs file. builder.Services.ConfigureApplicationCookie(options => { options.AccessDeniedPath = "/Identity/Account/AccessDenied"; // Customize this path as per your application's structure }); Using this way you will implement the role-based authorization in your application. Conclusion  By properly implementing authorization in your applications, you can ensure that resources and sensitive information are accessible only to authorized users. Remember to choose the appropriate authorization technique based on your application’s requirements and complexity.