Implementing Passwordless Authentication in ASP NET Core Identity

passwordless-token-provider.md

Implementing Passwordless Authentication in ASP.NET Core Identity

To allow a user login with a magic URL, you need to implement a custom token provider. I'll show you how to add a custom token provider to authenticate a user with a link.

Step-1

Create a class named PasswordlessLoginProvider in your *.Web project.

PasswordlessLoginProvider.cs

public class PasswordlessLoginProvider<TUser> : TotpSecurityStampBasedTokenProvider<TUser>
        where TUser : class
    {
        public override Task<bool> CanGenerateTwoFactorTokenAsync(UserManager<TUser> manager, TUser user)
        {
            return Task.FromResult(false);
        }

        public override async Task<string> GetUserModifierAsync(string purpose, UserManager<TUser> manager, TUser user)
        {
            var userId = await manager.GetUserIdAsync(user);

            return "PasswordlessLogin:" + purpose + ":" + userId;
        }
    }

Step-2

Create IdentityBuilderExtensions.cs in your *.Web project.

We will use this extension method in ConfigureServices.

public static class IdentityBuilderExtensions
{
    public static IdentityBuilder AddPasswordlessLoginProvider(this IdentityBuilder builder)
    {
        var userType = builder.UserType;
        var totpProvider = typeof(PasswordlessLoginProvider<>).MakeGenericType(userType);
        return builder.AddTokenProvider("PasswordlessLoginProvider", totpProvider);
    }
}

Step-3

Add the token provider to the Identity middleware. To do this, find the module class (eg: YourProjectWebModule.cs) in your *.Web project and add the below into the ConfigureServices() method.

public override void ConfigureServices(ServiceConfigurationContext context)
{
	//...
	context.Services
		.GetObject<IdentityBuilder>()
		.AddDefaultTokenProviders()
		.AddPasswordlessLoginProvider();
}

Step-4

We need to create a user interface to be able to generate the magic login link. To do this quickly, open your existing Index.cshtml.cs in your *.Web project. It's under Pages folder. And copy-paste the below content.

Index.cshtml.cs

public class IndexModel : MyBookStorePageModel
{
	protected IdentityUserManager UserManager { get; }

	private readonly IIdentityUserRepository _userRepository;

	public string PasswordlessLoginUrl { get; set; }

	public string Email { get; set; }

	public IndexModel(IdentityUserManager userManager, IIdentityUserRepository userRepository)
	{
		UserManager = userManager;
		_userRepository = userRepository;
	}

	public ActionResult OnGet()
	{
		if (!CurrentUser.IsAuthenticated)
		{
			return Redirect("/Account/Login");
		}

		return Page();
	}

	//added for passwordless authentication
	public async Task<IActionResult> OnPostGeneratePasswordlessTokenAsync()
	{
		var adminUser = await _userRepository.FindByNormalizedUserNameAsync("admin");

		var token = await UserManager.GenerateUserTokenAsync(adminUser, "PasswordlessLoginProvider", "passwordless-auth");

		PasswordlessLoginUrl = Url.Action("Login", "Passwordless", new { token = token, userId = adminUser.Id.ToString() }, Request.Scheme);

		return Page();
	}
}

We added OnPostGeneratePasswordlessTokenAsync() action to generate the link. We will generate a link for the admin user. Therefore, we injected IIdentityUserRepository to get admin user Id. Using the UserManager.GenerateUserTokenAsync() method, we generated a token. After that, we created the URL with the admin user Id and the token. Now we will show the PasswordlessLoginUrl on the page.

Step-5

Open your Index.cshtml and set the content as below. We added a form that posts to GeneratePasswordlessToken action in the razor page. And it will set the PasswordlessLoginUrl field.

@page
@inherits MyBookStore.Web.Pages.MyBookStorePage
@using MyBookStore.Web.Menus
@using Volo.Abp.AspNetCore.Mvc.UI.Layout
@model MyBookStore.Web.Pages.IndexModel
@{
    ViewBag.PageTitle = "Home";
}
@inject IPageLayout PageLayout
@{
    PageLayout.Content.Title = L["Home"].Value;
    PageLayout.Content.BreadCrumb.Add(L["Menu:Home"].Value);
    PageLayout.Content.MenuItemName = MyBookStoreMenus.Home;
}
<abp-card>
    <abp-card-body>
        <form asp-page-handler="GeneratePasswordlessToken" method="post">

            <abp-button button-type="Dark" type="submit">Generate passwordless token link</abp-button>

            @if (Model.PasswordlessLoginUrl != null)
            {
                <abp-card class="mt-3 p-3">
                    <a href="@Model.PasswordlessLoginUrl">@Model.PasswordlessLoginUrl</a>
                </abp-card>
            }
        </form>
    </abp-card-body>
</abp-card>

Step-6

We implemented token generation infrastructure, now it's time validate the token and let the user in. To do this create a folder named Controllers in your *.Web project and add the below controller.

PasswordlessController.cs

public class PasswordlessController : AbpController
{
	protected IdentityUserManager UserManager { get; }

	public PasswordlessController(IdentityUserManager userManager)
	{
		UserManager = userManager;
	}

	public virtual async Task<IActionResult> Login(string token, string userId)
	{
		var user = await UserManager.FindByIdAsync(userId);

		var isValid = await UserManager.VerifyUserTokenAsync(user, "PasswordlessLoginProvider", "passwordless-auth", token);
		if (!isValid)
		{
			throw new UnauthorizedAccessException("The token " + token + " is not valid for the user " + userId);
		}

		await UserManager.UpdateSecurityStampAsync(user);

		var roles = await UserManager.GetRolesAsync(user);

		var principal = new ClaimsPrincipal(
			new ClaimsIdentity(CreateClaims(user, roles), IdentityConstants.ApplicationScheme)
		);

		await HttpContext.SignInAsync(IdentityConstants.ApplicationScheme, principal);

		return Redirect("/");

	}

	private static IEnumerable<Claim> CreateClaims(IUser user, IEnumerable<string> roles)
	{
		var claims = new List<Claim>
		{
			new Claim("sub", user.Id.ToString()),
			new Claim(AbpClaimTypes.UserId, user.Id.ToString()),
			new Claim(AbpClaimTypes.Email, user.Email),
			new Claim(AbpClaimTypes.UserName, user.UserName),
			new Claim(AbpClaimTypes.EmailVerified, user.EmailConfirmed.ToString().ToLower()),
		};

		if (!string.IsNullOrWhiteSpace(user.PhoneNumber))
		{
			claims.Add(new Claim(AbpClaimTypes.PhoneNumber, user.PhoneNumber));
		}

		foreach (var role in roles)
		{
			claims.Add(new Claim(AbpClaimTypes.Role, role));
		}

		return claims;
	}
}

We created an endpoint for /Passwordless/Login that gets the token and the user Id. In this action, we find the user via repository and validating the token via UserManager.VerifyUserTokenAsync() method. If it's valid, we create claims of the user then call HttpContext.SignInAsync to be able to create an encrypted cookie and add it to the current response. Finally we redirect the page to the root URL.

That's all! We created a passwordless login with 6 steps.

You can also create the links with a lifetime so that it'll not be active forever. To do this check out this page.