Identity in ASP.NET Core – 40 questions

September 7, 2023 | by Meir Achildiev

40 questions and answers regarding Identity in ASP.NET Core:

What is ASP.NET Core Identity?
ASP.NET Core Identity is a membership system which allows you to add login functionality to your application. Users can create an account and sign in through a variety of providers. ASP.NET Core Identity provides features for password hashing, password policy enforcement, OAuth 2.0, Two-Factor Authentication (2FA), account confirmation, claims management, and more.
How do you create an ASP.NET Core application with Identity?
You can use the .NET CLI or Visual Studio to create a new ASP.NET Core project with Identity:

   dotnet new webapp --auth Individual

This command creates an ASP.NET Core Razor Pages application with Individual User Accounts.

How do you add Identity to an existing project?
First, you need to install the Identity package:

   dotnet add package Microsoft.AspNetCore.Identity.EntityFrameworkCore

Then, create a new User class:

   public class ApplicationUser : IdentityUser
   {
   }

And then create a new context class:

   public class ApplicationDbContext : IdentityDbContext<ApplicationUser>
   {
       public ApplicationDbContext(DbContextOptions<ApplicationDbContext> options)
           : base(options)
       {
       }
   }

Finally, register the context and the Identity services in Startup.cs:

   services.AddDbContext<ApplicationDbContext>(options =>
       options.UseSqlServer(Configuration.GetConnectionString("DefaultConnection")));

   services.AddDefaultIdentity<ApplicationUser>()
       .AddEntityFrameworkStores<ApplicationDbContext>();

How do you handle password complexity rules in Identity?
You can configure the password complexity rules in the Startup.cs file:

   services.Configure<IdentityOptions>(options =>
   {
       // Password settings.
       options.Password.RequireDigit = true;
       options.Password.RequireLowercase = true;
       options.Password.RequireNonAlphanumeric = true;
       options.Password.RequireUppercase = true;
       options.Password.RequiredLength = 6;
       options.Password.RequiredUniqueChars = 1;
   });

How do you enable Two-Factor Authentication in Identity?
You can enable Two-Factor Authentication (2FA) in Identity by setting the TwoFactorEnabled property to true:

   var user = await _userManager.GetUserAsync(User);
   await _userManager.SetTwoFactorEnabledAsync(user, true);

Then, you need to verify the second factor (e.g., a verification code sent via SMS or email).

How do you customize the Identity user model?
You can extend the IdentityUser class to include additional properties:

   public class ApplicationUser : IdentityUser
   {
       public string FullName { get; set; }
   }

Then use your ApplicationUser class instead of IdentityUser.

How do you add custom claims to the Identity user?
You can add custom claims to a user with the UserManager class:

   var claim = new Claim("DateOfBirth", "1970-01-01");
   var result = await _userManager.AddClaimAsync(user, claim);

How do you check if a user is in a role?
You can use the UserManager class to check if a user is in a role:

   var isInRole = await _userManager.IsInRoleAsync(user, "Admin");

How do you create roles in Identity?
You can use the RoleManager class to create roles:

   var role = new IdentityRole("Admin");
   var result = await _roleManager.CreateAsync(role);

How do you add a user to a role?
You can use the UserManager class to add a user to a role:

   var result = await _userManager.AddToRoleAsync(user, "Admin");

How do you remove a user from a role?
You can use the UserManager class to remove a user from a role:

   var result = await _userManager.RemoveFromRoleAsync(user, "Admin");

How do you use the [Authorize] attribute with roles?
You can restrict access to a controller or action to users with a specific role:

   [Authorize(Roles = "Admin")]
   public class AdminController : Controller
   {
       // ...
   }

How do you register a user in Identity?
You can use the UserManager class to register a user:

   var user = new ApplicationUser { UserName = model.Email, Email = model.Email };
   var result = await _userManager.CreateAsync(user, model.Password);

How do you sign in a user in Identity?
You can use the SignInManager class to sign in a user:

   var result = await _signInManager.PasswordSignInAsync(model.Email, model.Password, model.RememberMe, lockoutOnFailure: false);

How do you sign out a user in Identity?
You can use the SignInManager class to sign out a user:

   await _signInManager.SignOutAsync();

How do you enable email confirmation in Identity?
First, generate a confirmation token for a user:

   var code = await _userManager.GenerateEmailConfirmationTokenAsync(user);

Then, send the token to the user via email. The user clicks the link and is redirected to your app, where you confirm their email:

   var result = await _userManager.ConfirmEmailAsync(user, code);

How do you enable password reset in Identity?
First, generate a password reset token for a user:

   var code = await _userManager.GeneratePasswordResetTokenAsync(user);

Then, send the token to the user via email. The user clicks the link and is redirected to your app, where they can reset their password:

   var result = await _userManager.ResetPasswordAsync(user, code, model.Password);

How do you change a user’s password in Identity?
You can use the UserManager class to change a user’s password:

   var result = await _userManager.ChangePasswordAsync(user, model.OldPassword, model.NewPassword);

How do you customize the Identity UI?
You can scaffold the Identity views and modify them:

   dotnet aspnet-codegenerator identity --useDefaultUI

Then, you can modify the generated Razor views in the Areas/Identity/Pages directory.

How do you lock out a user in Identity?
You can use the UserManager class to lock out a user:

   var result = await _userManager.SetLockoutEndDateAsync(user, DateTimeOffset.UtcNow.AddMinutes(15));

How do you check if a user is locked out in Identity?
You can use the UserManager class to check if a user is locked out:

   var isLockedOut = await _userManager.IsLockedOutAsync(user);

How do you disable user lockout in Identity?
You can configure the lockout settings in Startup.cs:

   services.Configure<IdentityOptions>(options =>
   {
       options.Lockout.AllowedForNewUsers = false;
   });

How do you use policy-based authorization in Identity?
First, define a policy in Startup.cs:

   services.AddAuthorization(options =>
   {
       options.AddPolicy("AtLeast18", policy => policy.Requirements.Add(new MinimumAgeRequirement(18)));
   });

Then, create a AuthorizationHandler for the MinimumAgeRequirement:

   public class MinimumAgeHandler : AuthorizationHandler<MinimumAgeRequirement>
   {
       protected override Task HandleRequirementAsync(AuthorizationHandlerContext context, MinimumAgeRequirement requirement)
       {
           if (context.User.HasClaim(c => c.Type == ClaimTypes.DateOfBirth))
           {
               var dateOfBirth = Convert.ToDateTime(context.User.FindFirst(c => c.Type == ClaimTypes.DateOfBirth).Value);
               var age = DateTime.Today.Year - dateOfBirth.Year;

               if (age >= requirement.MinimumAge)
               {
                   context.Succeed(requirement);
               }
           }

           return Task.CompletedTask;
       }
   }

Finally, apply the policy to a controller or action:

   [Authorize(Policy = "AtLeast18")]
   public class AccountController : Controller
   {
       // ...
   }

How do you use external authentication providers in Identity?
You can configure external authentication providers (such as Google, Facebook, Twitter, etc.) in Startup.cs:

   services.AddAuthentication()
       .AddGoogle(options =>
       {
           options.ClientId = Configuration["Authentication:Google:ClientId"];
           options.ClientSecret = Configuration["Authentication:Google:ClientSecret"];
       });

Then, you can add a button to your login page to sign in with Google:

   <a class="btn btn-primary" href="/Identity/Account/ExternalLogin?provider=Google&returnUrl=%2F">Sign in with Google</a>

How do you handle email verification for external logins in Identity?
After a user signs in with an external provider, you can ask them to confirm their email:

   var info = await _signInManager.GetExternalLoginInfoAsync();
   var email = info.Principal.FindFirstValue(ClaimTypes.Email);

   var user = new ApplicationUser { UserName = email, Email = email };
   var result = await _userManager.CreateAsync(user);

   if (result.Succeeded)
   {
       var code = await _userManager.GenerateEmailConfirmationTokenAsync(user);
       // Send the email confirmation code
   }

How do you customize the Identity cookie?
You can customize the Identity cookie in Startup.cs:

   services.ConfigureApplicationCookie(options =>
   {
       options.Cookie.HttpOnly = true;
       options.ExpireTimeSpan = TimeSpan.FromMinutes(60);
       options.LoginPath = "/Identity/Account/Login";
       options.LogoutPath = "/Identity/Account/Logout";
   });

How do you add custom validators in Identity?
You can create a class that implements IUserValidator<ApplicationUser> or IPasswordValidator<ApplicationUser>:

   public class CustomUserValidator : IUserValidator<ApplicationUser>
   {
       public Task<IdentityResult> ValidateAsync(UserManager<ApplicationUser> manager, ApplicationUser user)
       {
           if (user.Email.ToLower().EndsWith("@example.com"))
           {
               return Task.FromResult(IdentityResult.Failed(new IdentityError
               {
                   Code = "EmailDomainError",
                   Description = "Only example.com email addresses are allowed",
               }));
           }
           else
           {
               return Task.FromResult(IdentityResult.Success);
           }
       }
   }

Then, register your custom validator in Startup.cs:

   services.AddTransient<IUserValidator<ApplicationUser>, CustomUserValidator>();

How do you handle account lockout in Identity?
You can configure the account lockout settings in Startup.cs:

   services.Configure<IdentityOptions>(options =>
   {
       options.Lockout.DefaultLockoutTimeSpan = TimeSpan.FromMinutes(5);
       options.Lockout.MaxFailedAccessAttempts = 5;
       options.Lockout.AllowedForNewUsers = true;
   });

Then, handle account lockout in your login action:

   var result = await _signInManager.PasswordSignInAsync(model.Email, model.Password, model.RememberMe, lockoutOnFailure: true);

   if (result.IsLockedOut)
   {
       _logger.LogWarning("User account locked out.");
       return RedirectToPage("./Lockout");
   }

How do you set up password recovery in Identity?
First, generate a password reset token for a user:

   var code = await _userManager.GeneratePasswordResetTokenAsync(user);

Then, send the token to the user via email. The user clicks the link and is redirected to your app, where they can reset their password:

   var result = await _userManager.ResetPasswordAsync(user, code, model.Password);

How do you enable account confirmation in Identity?
First, generate an email confirmation token for a user:

   var code = await _userManager.GenerateEmailConfirmationTokenAsync(user);

Then, send the token to the user via email. The user clicks the link and is redirected to your app, where you confirm their email:

   var result = await _userManager.ConfirmEmailAsync(user, code);

How do you handle username uniqueness in Identity?
By default, Identity ensures that usernames are unique. When you try to create a user with a username that already exists, UserManager.CreateAsync returns an IdentityResult with a Succeeded property of false:

   var user = new ApplicationUser { UserName = model.Email, Email = model.Email };
   var result = await _userManager.CreateAsync(user, model.Password);

   if (!result.Succeeded)
   {
       foreach (var error in result.Errors)
       {
           ModelState.AddModelError(string.Empty, error.Description);
       }
   }

How do you handle email uniqueness in Identity?
You can configure Identity to require unique emails in Startup.cs:

   services.Configure<IdentityOptions>(options =>
   {
       options.User.RequireUniqueEmail = true;
   });

How do you use JWT authentication with Identity? You can configure JWT authentication in Startup.cs:

   services.AddAuthentication(options =>
   {
       options.DefaultAuthenticateScheme = JwtBearerDefaults.AuthenticationScheme;
       options.DefaultChallengeScheme = JwtBearerDefaults.AuthenticationScheme;
   })
   .AddJwtBearer(options =>
   {
       options.TokenValidationParameters = new TokenValidationParameters
       {
           ValidateIssuerSigningKey = true,
           IssuerSigningKey = new SymmetricSecurityKey(Encoding.UTF8.GetBytes(Configuration["Jwt:Key"])),
           ValidateIssuer = false,
           ValidateAudience = false,
       };
   });

Then, generate a JWT when a user logs in:

   var claims = new[]
   {
       new Claim(JwtRegisteredClaimNames.Sub, user.UserName),
       new Claim(JwtRegisteredClaimNames.Jti, Guid.NewGuid().ToString()),
   };

   var key = new SymmetricSecurityKey(Encoding.UTF8.GetBytes(Configuration["Jwt:Key"]));
   var creds = new SigningCredentials(key, SecurityAlgorithms.HmacSha256);

   var token = new JwtSecurityToken(
       issuer: Configuration["Jwt:Issuer"],
       audience: Configuration["Jwt:Issuer"],
       claims: claims,
       expires: DateTime.Now.AddMinutes(30),
       signingCredentials: creds);

   return new JwtSecurityTokenHandler().WriteToken(token);

How do you sign out a user in Identity?
You can sign out a user using SignInManager:

   await _signInManager.SignOutAsync();

How do you handle two-factor authentication in Identity?
First, enable two-factor authentication for a user:

   var result = await _userManager.SetTwoFactorEnabledAsync(user, true);

Then, when a user logs in, send them a two-factor code:

   var code = await _userManager.GenerateTwoFactorTokenAsync(user, provider);

Finally, verify the code when the user submits it:

   var result = await _signInManager.TwoFactorSignInAsync(provider, model.Code, isPersistent: false, rememberClient: false);

How do you add custom user claims in Identity?
You can add custom user claims using UserManager:

   var claim = new Claim("Department", "Engineering");
   var result = await _userManager.AddClaimAsync(user, claim);

How do you check a user’s role in Identity?
You can check a user’s role using UserManager:

   var isInRole = await _userManager.IsInRoleAsync(user, "Admin");

How do you check a user’s claim in Identity?
You can check a user’s claim by examining the ClaimsIdentity:

   var identity = (ClaimsIdentity)User.Identity;
   var hasClaim = identity.HasClaim(c => c.Type == "Department" && c.Value == "Engineering");

How do you delete a user in Identity?
You can delete a user using UserManager:

   var result = await _userManager.DeleteAsync(user);

How do you update a user’s password in Identity?
You can update a user’s password using UserManager:

   var result = await _userManager.ChangePasswordAsync(user, model.CurrentPassword, model.NewPassword);

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