Jul 8

Written by: Michael Washington
7/8/2019 9:39 PM  RssIcon

 

To demonstrate how authentication works in a server-side Blazor application, we will strip authentication down to its most basic elements. We will simply set a cookie then read that cookie in the application.

 

Application Authentication

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Most business web applications require their users to log into the application.

 

image

The user enters their username and password, that are checked against a membership database.

 

image

Once authenticated, the application recognizes the user and now has the ability to deliver content securely.

Once the authentication process of a server-side Blazor application is understood, we can then implement an authentication and membership management system that meets our needs (for example, one that allows users to create and manage their user accounts).

NOTE: This sample code does not check to see if a person is using a legitimate username and password! You would need to add the proper code to check. This code is just a demonstration of how the process of authorizing a user works.

For a complete application see: Creating A Step-By-Step End-To-End Database Server-Side Blazor Application.

 

Create The Application

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Open Visual Studio 2019.

image

Create a Server side Blazor application without authentication.

 

Add Nuget Packages

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In the Solution Explorer, right-click on the client project and select Manage NuGet Packages.

 

image

Add references to the following libraries:

  • Microsoft.AspNetCore.Authorization
  • Microsoft.AspNetCore.Http
  • Microsoft.AspNetCore.Identity

 

Add Cookie Authentication

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Open the Startup.cs file.

Add the following using statements to the top of the file:

 

// ******
// BLAZOR COOKIE Auth Code (begin)
using Microsoft.AspNetCore.Authentication.Cookies;
using Microsoft.AspNetCore.Http;
using System.Net.Http;
// BLAZOR COOKIE Auth Code (end)
// ******
 

Alter the Startup class to the following, adding the sections marked BLAZOR COOKIE Auth Code:

 

    public class Startup
    {
        public Startup(IConfiguration configuration)
        {
            Configuration = configuration;
        }
        public IConfiguration Configuration { get; }
        public void ConfigureServices(IServiceCollection services)
        {
            // ******
            // BLAZOR COOKIE Auth Code (begin)
            services.Configure<CookiePolicyOptions>(options =>
            {
                options.CheckConsentNeeded = context => true;
                options.MinimumSameSitePolicy = SameSiteMode.None;
            });
            services.AddAuthentication(
                CookieAuthenticationDefaults.AuthenticationScheme)
                .AddCookie();
            // BLAZOR COOKIE Auth Code (end)
            // ******
            services.AddRazorPages();
            services.AddServerSideBlazor();
            services.AddSingleton<WeatherForecastService>();
            // ******
            // BLAZOR COOKIE Auth Code (begin)
            // From: https://github.com/aspnet/Blazor/issues/1554
            // HttpContextAccessor
            services.AddHttpContextAccessor();
            services.AddScoped<HttpContextAccessor>();
            services.AddHttpClient();
            services.AddScoped<HttpClient>();
            // BLAZOR COOKIE Auth Code (end)
            // ******
        }
        // This method gets called by the runtime. 
        // Use this method to configure the HTTP request pipeline.
        public void Configure(IApplicationBuilder app, IWebHostEnvironment env)
        {
            if (env.IsDevelopment())
            {
                app.UseDeveloperExceptionPage();
            }
            else
            {
                app.UseExceptionHandler("/Home/Error");
                app.UseHsts();
            }
            app.UseHttpsRedirection();
            app.UseStaticFiles();
            app.UseRouting();
            // ******
            // BLAZOR COOKIE Auth Code (begin)
            app.UseHttpsRedirection();
            app.UseStaticFiles();
            app.UseCookiePolicy();
            app.UseAuthentication();
            // BLAZOR COOKIE Auth Code (end)
            // ******
            app.UseEndpoints(endpoints =>
            {
                endpoints.MapBlazorHub();
                endpoints.MapFallbackToPage("/_Host");
            });
        }
    }

 

First the code adds support for cookies. Cookies are created by the application, and passed to the user’s web browser when the user logs in. The web browser passes the cookie back to the application to indicate that the user is authenticated. When the user ‘logs out’, the cookie is removed.

This code also adds:

  • HttpContextAccessor
  • HttpClient

as services that will be accessed in the code using dependency Injection.

See this link for a full explanation of how HttpContextAccessor allows us to determine who the logged in user is.

 

Add Login/Logout Pages

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Logging in (and out) is performed by .cshtml pages.

Add the following Razor pages and code:

 

Login.cshtml

 

@page
@model BlazorCookieAuth.Server.Pages.LoginModel
@{
    ViewData["Title"] = "Log in";
}
<h2>Login</h2>
 

 

Login.cshtml.cs

 

using System;
using System.Collections.Generic;
using System.Security.Claims;
using System.Threading.Tasks;
using Microsoft.AspNetCore.Authentication;
using Microsoft.AspNetCore.Authentication.Cookies;
using Microsoft.AspNetCore.Authorization;
using Microsoft.AspNetCore.Mvc;
using Microsoft.AspNetCore.Mvc.RazorPages;
namespace BlazorCookieAuth.Server.Pages
{
    [AllowAnonymous]
    public class LoginModel : PageModel
    {
        public string ReturnUrl { get; set; }
        public async Task<IActionResult> 
            OnGetAsync(string paramUsername, string paramPassword)
        {
            string returnUrl = Url.Content("~/");
            try
            {
                // Clear the existing external cookie
                await HttpContext
                    .SignOutAsync(
                    CookieAuthenticationDefaults.AuthenticationScheme);
            }
            catch { }
            // *** !!! This is where you would validate the user !!! ***
            // In this example we just log the user in
            // (Always log the user in for this demo)
            var claims = new List<Claim>
            {
                new Claim(ClaimTypes.Name, paramUsername),
                new Claim(ClaimTypes.Role, "Administrator"),
            };
            var claimsIdentity = new ClaimsIdentity(
                claims, CookieAuthenticationDefaults.AuthenticationScheme);
            var authProperties = new AuthenticationProperties
            {
                IsPersistent = true,
                RedirectUri = this.Request.Host.Value
            };
            try
            {
                await HttpContext.SignInAsync(
                CookieAuthenticationDefaults.AuthenticationScheme,
                new ClaimsPrincipal(claimsIdentity),
                authProperties);
            }
            catch (Exception ex)
            {
                string error = ex.Message;
            }
            return LocalRedirect(returnUrl);
        }
    }
}

 

Logout.cshtml

 

@page
@model BlazorCookieAuth.Server.Pages.LogoutModel
@{
    ViewData["Title"] = "Logout";
}
<h2>Logout</h2>

 

Logout.cshtml.cs

 

using System;
using System.Threading.Tasks;
using Microsoft.AspNetCore.Authentication;
using Microsoft.AspNetCore.Authentication.Cookies;
using Microsoft.AspNetCore.Mvc;
using Microsoft.AspNetCore.Mvc.RazorPages;
namespace BlazorCookieAuth.Server.Pages
{
    public class LogoutModel : PageModel
    {
        public async Task<IActionResult> OnGetAsync()
        {
            // Clear the existing external cookie
            await HttpContext
                .SignOutAsync(
                CookieAuthenticationDefaults.AuthenticationScheme);
            return LocalRedirect(Url.Content("~/"));
        }
    }
}

 

Add Client Code

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Add a page called LoginControl.razor to the Shared folder using the following code:

 

@page "/loginControl"
<AuthorizeView>
    <Authorized>
        <b>Hello, @context.User.Identity.Name!</b>
        <a class="ml-md-auto btn btn-primary"
           href="/logout?returnUrl=/"
           target="_top">Logout</a>
    </Authorized>
    <NotAuthorized>
        <input type="text"
               placeholder="User Name"
               @bind="@Username" />
        &nbsp;&nbsp;
        <input type="password"
               placeholder="Password"
               @bind="@Password" />
        <a class="ml-md-auto btn btn-primary"
           href="/login?paramUsername=@Username&paramPassword=@Password"
           target="_top">Login</a>
    </NotAuthorized>
</AuthorizeView>
@code {
    string Username = "";
    string Password = "";
}

 

This code creates a login component that uses the AuthorizeView component to wrap markup code based on the user’s current authentication.

If the user is logged in, we display their name and a Logout button (that navigates the user to the logout page created earlier).

If they are not logged in, we display username and password boxes and a Login button (that navigates the user to the login page created earlier).

 

image

Finally, we alter the MainLayout.razor page (in the Shared folder) to the following:

 

@inherits LayoutComponentBase
<div class="sidebar">
    <NavMenu />
</div>
<div class="main">
    <div class="top-row px-4">
        <!-- BLAZOR COOKIE Auth Code (begin) -->
        <LoginControl />
        <!-- BLAZOR COOKIE Auth Code (end) -->
    </div>
    <div class="content px-4">
        @Body
    </div>
</div>

 

This adds the login component to the top of every page in the Blazor application.

 

image

We can now hit F5 to run the application.

 

image

We can enter a username and password and click the Login button…

 

image

We can then look in the Google Chrome Web Browser DevTools and see the cookie has been created.

 

image

When we click Logout

 

image

The cookie is removed.

 

Calling Server Side Controller Methods

At this point all the .razor pages will properly detect if the user is authenticated, and operate as expected. However, if we make a http request to a server side controller, the authenticated user will not be properly detected.

 

image

To demonstrate this, we first open the startup.cs page and add the following code to the end of the app.UseEndpoints method, (under the endpoints.MapFallbackToPage("/_Host"); line), to allow http requests to controllers to be properly routed:

 

        // ******
        // BLAZOR COOKIE Auth Code (begin)
        endpoints.MapControllerRoute("default", "{controller=Home}/{action=Index}/{id?}");
        // BLAZOR COOKIE Auth Code (end)
        // ******

 

 

image

Next, we create a Controllers folder and add a UserController.cs file with the following code:

 

using Microsoft.AspNetCore.Mvc;
namespace BlazorCookieAuth.Controllers
{
    [Route("api/[controller]")]
    [ApiController]
    public class UserController : Controller
    {
        // /api/User/GetUser
        [HttpGet("[action]")]
        public UserModel GetUser()
        {
            // Instantiate a UserModel
            var userModel = new UserModel
            {
                UserName = "[]",
                IsAuthenticated = false
            };
            // Detect if the user is authenticated
            if (User.Identity.IsAuthenticated)
            {
                // Set the username of the authenticated user
                userModel.UserName = 
                    User.Identity.Name;
                userModel.IsAuthenticated = 
                    User.Identity.IsAuthenticated;
            };
            return userModel;
        }
    }
    // Class to hold the UserModel
    public class UserModel
    {
        public string UserName { get; set; }
        public bool IsAuthenticated { get; set; }
    }
}

 

image

We add a new .razor page, CallServerSide.razor, using the following code:

 

@page "/CallServerSide"
@using BlazorCookieAuth.Controllers
@using System.Net.Http
@inject HttpClient Http
@inject IUriHelper UriHelper
@inject Microsoft.AspNetCore.Http.IHttpContextAccessor HttpContextAccessor
<h3>Call Server Side</h3>
<p>Current User: @CurrentUser.UserName</p>
<p>IsAuthenticated: @CurrentUser.IsAuthenticated</p>
<button class="btn btn-primary" @onclick="@GetUser">Get User</button>
@code {
    UserModel CurrentUser = new UserModel();
    async Task GetUser()
    {
        // Call the server side controller
        var url = UriHelper.ToAbsoluteUri("/api/User/GetUser");
        var result = await Http.GetJsonAsync<UserModel>(url.ToString());
        // Update the result
        CurrentUser.UserName = result.UserName;
        CurrentUser.IsAuthenticated = result.IsAuthenticated;
    }
}

 

Finally, we use the following code to add a link to the page in Shared/NavMenu.razor:

 

        <li class="nav-item px-3">
            <NavLink class="nav-link" href="CallServerSide">
                <span class="oi oi-list-rich" aria-hidden="true"></span> Call Server Side
            </NavLink>
        </li>

 

 

 

image

We run the application and log in.

 

image

We navigate to the new Call Server Side control and click the Get User button (that calls the UserController.cs that we just added), and it does not detect the logged in user.

To resolve this, change the GetUser method in the CallServerSide.razor page to the following:

 

    async Task GetUser()
    {
        // Code courtesy from Oqtane.org (@sbwalker)
        // We must pass the authentication cookie in server side requests
        var authToken =
        HttpContextAccessor.HttpContext.Request.Cookies[".AspNetCore.Cookies"];
        if (authToken != null)
        {
            Http.DefaultRequestHeaders
            .Add("Cookie", ".AspNetCore.Cookies=" + authToken);
            // Call the server side controller
            var url = UriHelper.ToAbsoluteUri("/api/User/GetUser");
            var result = await Http.GetJsonAsync<UserModel>(url.ToString());
            // Update the result
            CurrentUser.UserName = result.UserName;
            CurrentUser.IsAuthenticated = result.IsAuthenticated;
        }
    }

 

We have an authentication cookie, we just need to pass it in the DefaultRequestHeaders.

 

image

Now, when we log in, and click the Get User button, the controller method is able to detect the logged in user.

 

Why Are We Using A Redirect Login Page?

When we look at the Blazor source code, at the page at this link, we see:

image

 

An AuthenticationStateProvider intended for use in server-side
Blazor. The circuit factory will supply a ClaimsPrincipal from
the current HttpContext.User, which will stay fixed for the
lifetime of the circuit since HttpContext.User cannot change.

This can therefore only be used with redirect-style authentication flows,
since it requires a new HTTP request in order to become a different user.

 

This indicates that the HttpContext.User that we are setting using the following code:

 

    await HttpContext.SignInAsync(
    CookieAuthenticationDefaults.AuthenticationScheme,
    new ClaimsPrincipal(claimsIdentity),
    authProperties);

 

Can only be set if we start a new http request. This is achieved by redirecting the user to the page that sets the user.

 

 

Special Thanks

This article would not be possible without sample code (using the full .Net Core Membership provider) provided by SQL-MisterMagoo.

Additional research provided by Shaun Walker.

 

Links

Blazor.net

Use cookie authentication without ASP.NET Core Identity

ASP.NET Core Blazor authentication and authorization

BlazorTest (SQL-MisterMagoo's site)

Authentication for serverside Blazor (How to use IHttpContextAccessor)

Blazor Security/Authorization

 

 

Download

The project is available at http://lightswitchhelpwebsite.com/Downloads.aspx

You must have Visual Studio 2019 (or higher) installed to run the code.

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