Secure a hosted ASP.NET Core Blazor WebAssembly app with Azure Active Directory B2C

This article explains how to create a hosted Blazor WebAssembly solution that uses Azure Active Directory (AAD) B2C for authentication.

For additional security scenario coverage after reading this article, see ASP.NET Core Blazor WebAssembly additional security scenarios.

Walkthrough

The subsections of the walkthrough explain how to:

  • Create a tenant in Azure
  • Register a server API app in Azure
  • Register a client app in Azure
  • Create the Blazor app
  • Modify the default access token scope scheme
  • Run the app

Create a tenant in Azure

Follow the guidance in Tutorial: Create an Azure Active Directory B2C tenant to create an AAD B2C tenant.

Before proceeding with this article's guidance, confirm that you've selected the correct directory for the AAD B2C tenant.

Register a server API app in Azure

Register an AAD B2C app for the Server API app:

  1. Navigate to Azure AD B2C in the Azure portal. Select App registrations in the sidebar. Select the New registration button.
  2. Provide a Name for the app (for example, Blazor Server AAD B2C).
  3. For Supported account types, select the multi-tenant option: Accounts in any identity provider or organizational directory (for authenticating users with user flows)
  4. The Server API app doesn't require a Redirect URI in this scenario, so leave the Select a platform dropdown list unselected and don't enter a redirect URI.
  5. Confirm that Permissions > Grant admin consent to openid and offline_access permissions is selected.
  6. Select Register.

Record the following information:

  • Server API app Application (client) ID (for example, 41451fa7-82d9-4673-8fa5-69eff5a761fd)
  • AAD B2C instance (for example, https://contoso.b2clogin.com/, which includes the trailing slash). The instance is the scheme and host of an Azure B2C app registration, which can be found by opening the Endpoints window from the App registrations page in the Azure portal.
  • Primary/Publisher/Tenant domain (for example, contoso.onmicrosoft.com): The domain is available as the Publisher domain in the Branding blade of the Azure portal for the registered app.

Select Expose an API from the sidebar and follow these steps:

  1. Select Add a scope.
  2. Select Save and continue.
  3. Provide a Scope name (for example, API.Access).
  4. Provide an Admin consent display name (for example, Access API).
  5. Provide an Admin consent description (for example, Allows the app to access server app API endpoints.).
  6. Confirm that the State is set to Enabled.
  7. Select Add scope.

Record the following information:

  • App ID URI GUID (for example, record 41451fa7-82d9-4673-8fa5-69eff5a761fd from https://contoso.onmicrosoft.com/41451fa7-82d9-4673-8fa5-69eff5a761fd)
  • Scope name (for example, API.Access)

Register a client app in Azure

Register an AAD B2C app for the Client app:

  1. Navigate to Azure AD B2C in the Azure portal. Select App registrations in the sidebar. Select the New registration button.
  2. Provide a Name for the app (for example, Blazor Client AAD B2C).
  3. For Supported account types, select the multi-tenant option: Accounts in any identity provider or organizational directory (for authenticating users with user flows)
  4. Set the Redirect URI dropdown list to Single-page application (SPA) and provide a redirect URI value of https://localhost/authentication/login-callback. If you know the production redirect URI for the Azure default host (for example, azurewebsites.net) or the custom domain host (for example, contoso.com), you can also add the production redirect URI at the same time that you're providing the localhost redirect URI. Be sure to include the port number for non-:443 ports in any production redirect URIs that you add.
  5. Confirm that Permissions > Grant admin consent to openid and offline_access permissions is selected.
  6. Select Register.

Note

Supplying the port number for a localhost AAD B2C redirect URI isn't required. For more information, see Redirect URI (reply URL) restrictions and limitations: Localhost exceptions (Entra documentation).

Record the Client app Application (client) ID (for example, 4369008b-21fa-427c-abaa-9b53bf58e538).

In Authentication > Platform configurations > Single-page application:

  1. Confirm the redirect URI of https://localhost/authentication/login-callback is present.
  2. In the Implicit grant section, ensure that the checkboxes for Access tokens and ID tokens aren't selected. Implicit grant isn't recommended for Blazor apps using MSAL v2.0 or later. For more information, see Secure ASP.NET Core Blazor WebAssembly.
  3. The remaining defaults for the app are acceptable for this experience.
  4. Select the Save button if you made changes.

In API permissions from the sidebar:

  1. Select Add a permission followed by My APIs.
  2. Select the Server API app from the Name column (for example, Blazor Server AAD B2C).
  3. Open the API list if it isn't already open.
  4. Enable access to the API (for example, API.Access) with the checkbox.
  5. Select Add permissions.
  6. Select the Grant admin consent for {TENANT NAME} button. Select Yes to confirm.

Important

If you don't have the authority to grant admin consent to the tenant in the last step of API permissions configuration because consent to use the app is delegated to users, then you must take the following additional steps:

  • The app must use a trusted publisher domain.
  • In the Server app's configuration in the Azure portal, select Expose an API. Under Authorized client applications, select the button to Add a client application. Add the Client app's Application (client) ID (for example, 4369008b-21fa-427c-abaa-9b53bf58e538).

Return to Azure AD B2C in the Azure portal. Select User flows and use the following guidance: Create a sign-up and sign-in user flow. At a minimum, select Application claims for the sign-up/sign-in user flow and then the Display Name user attribute checkbox to populate the context.User.Identity?.Name/context.User.Identity.Name in the LoginDisplay component (Shared/LoginDisplay.razor).

Record the sign-up and sign-in user flow name created for the app (for example, B2C_1_signupsignin1).

Create the Blazor app

Replace the placeholders in the following command with the information recorded earlier and execute the command in a command shell:

dotnet new blazorwasm -au IndividualB2C --aad-b2c-instance "{AAD B2C INSTANCE}" --api-client-id "{SERVER API APP CLIENT ID}" --app-id-uri "{SERVER API APP ID URI GUID}" --client-id "{CLIENT APP CLIENT ID}" --default-scope "{DEFAULT SCOPE}" --domain "{TENANT DOMAIN}" -ho -o {PROJECT NAME} -ssp "{SIGN UP OR SIGN IN POLICY}"

Warning

Avoid using dashes (-) in the app name {PROJECT NAME} that break the formation of the OIDC app identifier. Logic in the Blazor WebAssembly project template uses the project name for an OIDC app identifier in the solution's configuration. Pascal case (BlazorSample) or underscores (Blazor_Sample) are acceptable alternatives. For more information, see Dashes in a hosted Blazor WebAssembly project name break OIDC security (dotnet/aspnetcore #35337).

Placeholder Azure portal name Example
{AAD B2C INSTANCE} Instance https://contoso.b2clogin.com/ (includes the trailing slash)
{PROJECT NAME} BlazorSample
{CLIENT APP CLIENT ID} Application (client) ID for the Client app 4369008b-21fa-427c-abaa-9b53bf58e538
{DEFAULT SCOPE} Scope name API.Access
{SERVER API APP CLIENT ID} Application (client) ID for the Server app 41451fa7-82d9-4673-8fa5-69eff5a761fd
{SERVER API APP ID URI GUID} Application ID URI GUID 41451fa7-82d9-4673-8fa5-69eff5a761fd (GUID ONLY, by default matches the {SERVER API APP CLIENT ID})
{SIGN UP OR SIGN IN POLICY} Sign-up/sign-in user flow B2C_1_signupsignin1
{TENANT DOMAIN} Primary/Publisher/Tenant domain contoso.onmicrosoft.com

The output location specified with the -o|--output option creates a project folder if it doesn't exist and becomes part of the project's name. Avoid using dashes (-) in the app name that break the formation of the OIDC app identifier (see the earlier WARNING).

Run the app

Run the app from the Server project. When using Visual Studio, either:

  • Select the dropdown arrow next to the Run button. Open Configure Startup Projects from the dropdown list. Select the Single startup project option. Confirm or change the project for the startup project to the Server project.

  • Confirm that the Server project is highlighted in Solution Explorer before you start the app with any of the following approaches:

    • Select the Run button.
    • Use Debug > Start Debugging from the menu.
    • Press F5.
  • In a command shell, navigate to the Server project folder of the solution. Execute the dotnet run command.

Custom policies

The Microsoft Authentication Library (Microsoft.Authentication.WebAssembly.Msal, NuGet package) doesn't support AAD B2C custom policies by default.

Configure User.Identity.Name

The guidance in this section covers optionally populating User.Identity.Name with the value from the name claim.

By default, the Server app API populates User.Identity.Name with the value from the http://schemas.xmlsoap.org/ws/2005/05/identity/claims/name claim type (for example, 2d64b3da-d9d5-42c6-9352-53d8df33d770@contoso.onmicrosoft.com).

To configure the app to receive the value from the name claim type:

Parts of the solution

This section describes the parts of a solution generated from the Blazor WebAssembly project template and describes how the solution's Client and Server projects are configured for reference. There's no specific guidance to follow in this section for a basic working application if you created the app using the guidance in the Walkthrough section. The guidance in this section is helpful for updating an app to authenticate and authorize users. However, an alternative approach to updating an app is to create a new app from the guidance in the Walkthrough section and moving the app's components, classes, and resources to the new app.

appsettings.json configuration

This section pertains to the solution's Server app.

The appsettings.json file contains the options to configure the JWT bearer handler used to validate access tokens:

{
  "AzureAdB2C": {
    "Instance": "https://{TENANT}.b2clogin.com/",
    "ClientId": "{SERVER API APP CLIENT ID}",
    "Domain": "{TENANT DOMAIN}",
    "Scopes": "{DEFAULT SCOPE}",
    "SignUpSignInPolicyId": "{SIGN UP OR SIGN IN POLICY}"
  }
}

Example:

{
  "AzureAdB2C": {
    "Instance": "https://contoso.b2clogin.com/",
    "ClientId": "41451fa7-82d9-4673-8fa5-69eff5a761fd",
    "Domain": "contoso.onmicrosoft.com",
    "Scopes": "API.Access",
    "SignUpSignInPolicyId": "B2C_1_signupsignin1",
  }
}

Authentication package

This section pertains to the solution's Server app.

The support for authenticating and authorizing calls to ASP.NET Core web APIs with the Microsoft Identity Platform is provided by the Microsoft.Identity.Web package.

Note

For guidance on adding packages to .NET apps, see the articles under Install and manage packages at Package consumption workflow (NuGet documentation). Confirm correct package versions at NuGet.org.

The Server app of a hosted Blazor solution created from the Blazor WebAssembly template includes the Microsoft.Identity.Web.UI package by default. The package adds UI for user authentication in web apps and isn't used by the Blazor framework. If the Server app won't be used to authenticate users directly, it's safe to remove the package reference from the Server app's project file.

Authentication service support

This section pertains to the solution's Server app.

The AddAuthentication method sets up authentication services within the app and configures the JWT Bearer handler as the default authentication method. The AddMicrosoftIdentityWebApi method configures services to protect the web API with Microsoft Identity Platform v2.0. This method expects an AzureAdB2C section in the app's configuration with the necessary settings to initialize authentication options.

builder.Services.AddAuthentication(JwtBearerDefaults.AuthenticationScheme)
    .AddMicrosoftIdentityWebApi(Configuration.GetSection("AzureAdB2C"));

Note

When a single authentication scheme is registered, the authentication scheme is automatically used as the app's default scheme, and it isn't necessary to state the scheme to AddAuthentication or via AuthenticationOptions. For more information, see Overview of ASP.NET Core Authentication and the ASP.NET Core announcement (aspnet/Announcements #490).

UseAuthentication and UseAuthorization ensure that:

  • The app attempts to parse and validate tokens on incoming requests.
  • Any request attempting to access a protected resource without proper credentials fails.
app.UseAuthorization();

WeatherForecast controller

This section pertains to the solution's Server app.

The WeatherForecast controller (Controllers/WeatherForecastController.cs) exposes a protected API with the [Authorize] attribute applied to the controller. It's important to understand that:

  • The [Authorize] attribute in this API controller is the only thing that protects this API from unauthorized access.
  • The [Authorize] attribute used in the Blazor WebAssembly app only serves as a hint to the app that the user should be authorized for the app to work correctly.
[Authorize]
[ApiController]
[Route("[controller]")]
[RequiredScope(RequiredScopesConfigurationKey = "AzureAdB2C:Scopes")]
public class WeatherForecastController : ControllerBase
{
    [HttpGet]
    public IEnumerable<WeatherForecast> Get()
    {
        ...
    }
}

wwwroot/appsettings.json configuration

This section pertains to the solution's Client app.

Configuration is supplied by the wwwroot/appsettings.json file:

{
  "AzureAdB2C": {
    "Authority": "{AAD B2C INSTANCE}{TENANT DOMAIN}/{SIGN UP OR SIGN IN POLICY}",
    "ClientId": "{CLIENT APP CLIENT ID}",
    "ValidateAuthority": false
  }
}

In the preceding configuration, the {AAD B2C INSTANCE} includes a trailing slash.

Example:

{
  "AzureAdB2C": {
    "Authority": "https://contoso.b2clogin.com/contoso.onmicrosoft.com/B2C_1_signupsignin1",
    "ClientId": "4369008b-21fa-427c-abaa-9b53bf58e538",
    "ValidateAuthority": false
  }
}

Authentication package

This section pertains to the solution's Client app.

When an app is created to use an Individual B2C Account (IndividualB2C), the app automatically receives a package reference for the Microsoft Authentication Library (Microsoft.Authentication.WebAssembly.Msal). The package provides a set of primitives that help the app authenticate users and obtain tokens to call protected APIs.

If adding authentication to an app, manually add the Microsoft.Authentication.WebAssembly.Msal package to the app.

Note

For guidance on adding packages to .NET apps, see the articles under Install and manage packages at Package consumption workflow (NuGet documentation). Confirm correct package versions at NuGet.org.

The Microsoft.Authentication.WebAssembly.Msal package transitively adds the Microsoft.AspNetCore.Components.WebAssembly.Authentication package to the app.

Authentication service support

This section pertains to the solution's Client app.

Support for HttpClient instances is added that include access tokens when making requests to the server project.

In the Program file:

builder.Services.AddHttpClient("{PROJECT NAME}.ServerAPI", client => 
    client.BaseAddress = new Uri(builder.HostEnvironment.BaseAddress))
    .AddHttpMessageHandler<BaseAddressAuthorizationMessageHandler>();

builder.Services.AddScoped(sp => sp.GetRequiredService<IHttpClientFactory>()
    .CreateClient("{PROJECT NAME}.ServerAPI"));

The placeholder {PROJECT NAME} is the project name at solution creation. For example, providing a project name of BlazorSample produces a named HttpClient of BlazorSample.ServerAPI.

Support for authenticating users is registered in the service container with the AddMsalAuthentication extension method provided by the Microsoft.Authentication.WebAssembly.Msal package. This method sets up the services required for the app to interact with the Identity Provider (IP).

In the Program file:

builder.Services.AddMsalAuthentication(options =>
{
    builder.Configuration.Bind("AzureAdB2C", options.ProviderOptions.Authentication);
    options.ProviderOptions.DefaultAccessTokenScopes.Add("{SCOPE URI}");
});

The {SCOPE URI} is the default access token scope (for example, https://contoso.onmicrosoft.com/41451fa7-82d9-4673-8fa5-69eff5a761fd/API.Access or the custom URI that you configured in the Azure portal).

The AddMsalAuthentication method accepts a callback to configure the parameters required to authenticate an app. The values required for configuring the app can be obtained from the Azure Portal AAD configuration when you register the app.

Access token scopes

This section pertains to the solution's Client app.

The default access token scopes represent the list of access token scopes that are:

  • Included by default in the sign in request.
  • Used to provision an access token immediately after authentication.

All scopes must belong to the same app per Microsoft Entra ID rules. Additional scopes can be added for additional API apps as needed:

builder.Services.AddMsalAuthentication(options =>
{
    ...
    options.ProviderOptions.DefaultAccessTokenScopes.Add("{SCOPE URI}");
});

Specify additional scopes with AdditionalScopesToConsent:

options.ProviderOptions.AdditionalScopesToConsent.Add("{ADDITIONAL SCOPE URI}");

Example default access token scope:

options.ProviderOptions.DefaultAccessTokenScopes.Add(
    "https://contoso.onmicrosoft.com/41451fa7-82d9-4673-8fa5-69eff5a761fd/API.Access");

For more information, see the following sections of the Additional scenarios article:

Login mode

This section pertains to the solution's Client app.

The framework defaults to pop-up login mode and falls back to redirect login mode if a pop-up can't be opened. Configure MSAL to use redirect login mode by setting the LoginMode property of MsalProviderOptions to redirect:

builder.Services.AddMsalAuthentication(options =>
{
    ...
    options.ProviderOptions.LoginMode = "redirect";
});

The default setting is popup, and the string value isn't case-sensitive.

Imports file

This section pertains to the solution's Client app.

The Microsoft.AspNetCore.Components.Authorization namespace is made available throughout the app via the _Imports.razor file:

@using System.Net.Http
@using System.Net.Http.Json
@using Microsoft.AspNetCore.Components.Authorization
@using Microsoft.AspNetCore.Components.Forms
@using Microsoft.AspNetCore.Components.Routing
@using Microsoft.AspNetCore.Components.Web
@using Microsoft.AspNetCore.Components.Web.Virtualization
@using Microsoft.AspNetCore.Components.WebAssembly.Http
@using Microsoft.JSInterop
@using {APPLICATION ASSEMBLY}
@using {APPLICATION ASSEMBLY}.Shared

Index page

This section pertains to the solution's Client app.

The Index page (wwwroot/index.html) page includes a script that defines the AuthenticationService in JavaScript. AuthenticationService handles the low-level details of the OIDC protocol. The app internally calls methods defined in the script to perform the authentication operations.

<script src="_content/Microsoft.Authentication.WebAssembly.Msal/AuthenticationService.js"></script>

App component

This section pertains to the solution's Client app.

The App component (App.razor) is similar to the App component found in Blazor Server apps:

  • The CascadingAuthenticationState component manages exposing the AuthenticationState to the rest of the app.
  • The AuthorizeRouteView component makes sure that the current user is authorized to access a given page or otherwise renders the RedirectToLogin component.
  • The RedirectToLogin component manages redirecting unauthorized users to the login page.

Due to changes in the framework across releases of ASP.NET Core, Razor markup for the App component (App.razor) isn't shown in this section. To inspect the markup of the component for a given release, use either of the following approaches:

  • Create an app provisioned for authentication from the default Blazor WebAssembly project template for the version of ASP.NET Core that you intend to use. Inspect the App component (App.razor) in the generated app.

  • Inspect the App component (App.razor) in reference source. Select the version from the branch selector, and search for the component in the ProjectTemplates folder of the repository because it has moved over the years.

    Note

    Documentation links to .NET reference source usually load the repository's default branch, which represents the current development for the next release of .NET. To select a tag for a specific release, use the Switch branches or tags dropdown list. For more information, see How to select a version tag of ASP.NET Core source code (dotnet/AspNetCore.Docs #26205).

RedirectToLogin component

This section pertains to the solution's Client app.

The RedirectToLogin component (Shared/RedirectToLogin.razor):

  • Manages redirecting unauthorized users to the login page.
  • The current URL that the user is attempting to access is maintained by so that they can be returned to that page if authentication is successful using:

Inspect the RedirectToLogin component in reference source.

Note

Documentation links to .NET reference source usually load the repository's default branch, which represents the current development for the next release of .NET. To select a tag for a specific release, use the Switch branches or tags dropdown list. For more information, see How to select a version tag of ASP.NET Core source code (dotnet/AspNetCore.Docs #26205).

LoginDisplay component

This section pertains to the solution's Client app.

The LoginDisplay component (Shared/LoginDisplay.razor) is rendered in the MainLayout component (Shared/MainLayout.razor) and manages the following behaviors:

  • For authenticated users:
    • Displays the current user name.
    • Offers a link to the user profile page in ASP.NET Core Identity.
    • Offers a button to log out of the app.
  • For anonymous users:
    • Offers the option to register.
    • Offers the option to log in.

Due to changes in the framework across releases of ASP.NET Core, Razor markup for the LoginDisplay component isn't shown in this section. To inspect the markup of the component for a given release, use either of the following approaches:

  • Create an app provisioned for authentication from the default Blazor WebAssembly project template for the version of ASP.NET Core that you intend to use. Inspect the LoginDisplay component in the generated app.

  • Inspect the LoginDisplay component in reference source. The templated content for Hosted equal to true is used.

    Note

    Documentation links to .NET reference source usually load the repository's default branch, which represents the current development for the next release of .NET. To select a tag for a specific release, use the Switch branches or tags dropdown list. For more information, see How to select a version tag of ASP.NET Core source code (dotnet/AspNetCore.Docs #26205).

Authentication component

This section pertains to the solution's Client app.

The page produced by the Authentication component (Pages/Authentication.razor) defines the routes required for handling different authentication stages.

The RemoteAuthenticatorView component:

@page "/authentication/{action}"
@using Microsoft.AspNetCore.Components.WebAssembly.Authentication

<RemoteAuthenticatorView Action="Action" />

@code {
    [Parameter]
    public string? Action { get; set; }
}

Note

Nullable reference types (NRTs) and .NET compiler null-state static analysis is supported in ASP.NET Core in .NET 6 or later. Prior to the release of ASP.NET Core in .NET 6, the string type appears without the null type designation (?).

FetchData component

This section pertains to the solution's Client app.

The FetchData component shows how to:

  • Provision an access token.
  • Use the access token to call a protected resource API in the Server app.

The @attribute [Authorize] directive indicates to the Blazor WebAssembly authorization system that the user must be authorized in order to visit this component. The presence of the attribute in the Client app doesn't prevent the API on the server from being called without proper credentials. The Server app also must use [Authorize] on the appropriate endpoints to correctly protect them.

IAccessTokenProvider.RequestAccessToken takes care of requesting an access token that can be added to the request to call the API. If the token is cached or the service is able to provision a new access token without user interaction, the token request succeeds. Otherwise, the token request fails with an AccessTokenNotAvailableException, which is caught in a try-catch statement.

In order to obtain the actual token to include in the request, the app must check that the request succeeded by calling tokenResult.TryGetToken(out var token).

If the request was successful, the token variable is populated with the access token. The AccessToken.Value property of the token exposes the literal string to include in the Authorization request header.

If the request failed because the token couldn't be provisioned without user interaction:

  • ASP.NET Core in .NET 7 or later: The app navigates to AccessTokenResult.InteractiveRequestUrl using the given AccessTokenResult.InteractionOptions to allow refreshing the access token.
  • ASP.NET Core in .NET 6 or earlier: The token result contains a redirect URL. Navigating to this URL takes the user to the login page and back to the current page after a successful authentication.
@page "/fetchdata"
@using Microsoft.AspNetCore.Authorization
@using Microsoft.AspNetCore.Components.WebAssembly.Authentication
@using {APP NAMESPACE}.Shared
@attribute [Authorize]
@inject HttpClient Http

...

@code {
    private WeatherForecast[] forecasts;

    protected override async Task OnInitializedAsync()
    {
        try
        {
            forecasts = await Http.GetFromJsonAsync<WeatherForecast[]>("WeatherForecast");
        }
        catch (AccessTokenNotAvailableException exception)
        {
            exception.Redirect();
        }
    }
}

Troubleshoot

Logging

This section applies to ASP.NET Core in .NET 7 or later.

To enable debug or trace logging for Blazor WebAssembly authentication, see ASP.NET Core Blazor logging.

Common errors

  • Misconfiguration of the app or Identity Provider (IP)

    The most common errors are caused by incorrect configuration. The following are a few examples:

    • Depending on the requirements of the scenario, a missing or incorrect Authority, Instance, Tenant ID, Tenant domain, Client ID, or Redirect URI prevents an app from authenticating clients.
    • An incorrect access token scope prevents clients from accessing server web API endpoints.
    • Incorrect or missing server API permissions prevent clients from accessing server web API endpoints.
    • Running the app at a different port than is configured in the Redirect URI of the Identity Provider's app registration.

    Configuration sections of this article's guidance show examples of the correct configuration. Carefully check each section of the article looking for app and IP misconfiguration.

    If the configuration appears correct:

    • Analyze application logs.

    • Examine the network traffic between the client app and the IP or server app with the browser's developer tools. Often, an exact error message or a message with a clue to what's causing the problem is returned to the client by the IP or server app after making a request. Developer tools guidance is found in the following articles:

    • Decode the contents of a JSON Web Token (JWT) used for authenticating a client or accessing a server web API, depending on where the problem is occurring. For more information, see Inspect the content of a JSON Web Token (JWT).

    The documentation team responds to document feedback and bugs in articles (open an issue from the This page feedback section) but is unable to provide product support. Several public support forums are available to assist with troubleshooting an app. We recommend the following:

    The preceding forums are not owned or controlled by Microsoft.

    For non-security, non-sensitive, and non-confidential reproducible framework bug reports, open an issue with the ASP.NET Core product unit. Don't open an issue with the product unit until you've thoroughly investigated the cause of a problem and can't resolve it on your own and with the help of the community on a public support forum. The product unit isn't able to troubleshoot individual apps that are broken due to simple misconfiguration or use cases involving third-party services. If a report is sensitive or confidential in nature or describes a potential security flaw in the product that attackers may exploit, see Reporting security issues and bugs (dotnet/aspnetcore GitHub repository).

  • Unauthorized client for ME-ID

    info: Microsoft.AspNetCore.Authorization.DefaultAuthorizationService[2] Authorization failed. These requirements were not met: DenyAnonymousAuthorizationRequirement: Requires an authenticated user.

    Login callback error from ME-ID:

    • Error: unauthorized_client
    • Description: AADB2C90058: The provided application is not configured to allow public clients.

    To resolve the error:

    1. In the Azure portal, access the app's manifest.
    2. Set the allowPublicClient attribute to null or true.

Cookies and site data

Cookies and site data can persist across app updates and interfere with testing and troubleshooting. Clear the following when making app code changes, user account changes with the provider, or provider app configuration changes:

  • User sign-in cookies
  • App cookies
  • Cached and stored site data

One approach to prevent lingering cookies and site data from interfering with testing and troubleshooting is to:

  • Configure a browser
    • Use a browser for testing that you can configure to delete all cookie and site data each time the browser is closed.
    • Make sure that the browser is closed manually or by the IDE for any change to the app, test user, or provider configuration.
  • Use a custom command to open a browser in InPrivate or Incognito mode in Visual Studio:
    • Open Browse With dialog box from Visual Studio's Run button.
    • Select the Add button.
    • Provide the path to your browser in the Program field. The following executable paths are typical installation locations for Windows 10. If your browser is installed in a different location or you aren't using Windows 10, provide the path to the browser's executable.
      • Microsoft Edge: C:\Program Files (x86)\Microsoft\Edge\Application\msedge.exe
      • Google Chrome: C:\Program Files (x86)\Google\Chrome\Application\chrome.exe
      • Mozilla Firefox: C:\Program Files\Mozilla Firefox\firefox.exe
    • In the Arguments field, provide the command-line option that the browser uses to open in InPrivate or Incognito mode. Some browsers require the URL of the app.
      • Microsoft Edge: Use -inprivate.
      • Google Chrome: Use --incognito --new-window {URL}, where the placeholder {URL} is the URL to open (for example, https://localhost:5001).
      • Mozilla Firefox: Use -private -url {URL}, where the placeholder {URL} is the URL to open (for example, https://localhost:5001).
    • Provide a name in the Friendly name field. For example, Firefox Auth Testing.
    • Select the OK button.
    • To avoid having to select the browser profile for each iteration of testing with an app, set the profile as the default with the Set as Default button.
    • Make sure that the browser is closed by the IDE for any change to the app, test user, or provider configuration.

App upgrades

A functioning app may fail immediately after upgrading either the .NET Core SDK on the development machine or changing package versions within the app. In some cases, incoherent packages may break an app when performing major upgrades. Most of these issues can be fixed by following these instructions:

  1. Clear the local system's NuGet package caches by executing dotnet nuget locals all --clear from a command shell.
  2. Delete the project's bin and obj folders.
  3. Restore and rebuild the project.
  4. Delete all of the files in the deployment folder on the server prior to redeploying the app.

Note

Use of package versions incompatible with the app's target framework isn't supported. For information on a package, use the NuGet Gallery or FuGet Package Explorer.

Run the Server app

When testing and troubleshooting a hosted Blazor WebAssembly solution, make sure that you're running the app from the Server project.

Inspect the user

The following User component can be used directly in apps or serve as the basis for further customization.

User.razor:

@page "/user"
@attribute [Authorize]
@using System.Text.Json
@using System.Security.Claims
@inject IAccessTokenProvider AuthorizationService

<h1>@AuthenticatedUser?.Identity?.Name</h1>

<h2>Claims</h2>

@foreach (var claim in AuthenticatedUser?.Claims ?? Array.Empty<Claim>())
{
    <p class="claim">@(claim.Type): @claim.Value</p>
}

<h2>Access token</h2>

<p id="access-token">@AccessToken?.Value</p>

<h2>Access token claims</h2>

@foreach (var claim in GetAccessTokenClaims())
{
    <p>@(claim.Key): @claim.Value.ToString()</p>
}

@if (AccessToken != null)
{
    <h2>Access token expires</h2>

    <p>Current time: <span id="current-time">@DateTimeOffset.Now</span></p>
    <p id="access-token-expires">@AccessToken.Expires</p>

    <h2>Access token granted scopes (as reported by the API)</h2>

    @foreach (var scope in AccessToken.GrantedScopes)
    {
        <p>Scope: @scope</p>
    }
}

@code {
    [CascadingParameter]
    private Task<AuthenticationState> AuthenticationState { get; set; }

    public ClaimsPrincipal AuthenticatedUser { get; set; }
    public AccessToken AccessToken { get; set; }

    protected override async Task OnInitializedAsync()
    {
        await base.OnInitializedAsync();
        var state = await AuthenticationState;
        var accessTokenResult = await AuthorizationService.RequestAccessToken();

        if (!accessTokenResult.TryGetToken(out var token))
        {
            throw new InvalidOperationException(
                "Failed to provision the access token.");
        }

        AccessToken = token;

        AuthenticatedUser = state.User;
    }

    protected IDictionary<string, object> GetAccessTokenClaims()
    {
        if (AccessToken == null)
        {
            return new Dictionary<string, object>();
        }

        // header.payload.signature
        var payload = AccessToken.Value.Split(".")[1];
        var base64Payload = payload.Replace('-', '+').Replace('_', '/')
            .PadRight(payload.Length + (4 - payload.Length % 4) % 4, '=');

        return JsonSerializer.Deserialize<IDictionary<string, object>>(
            Convert.FromBase64String(base64Payload));
    }
}

Inspect the content of a JSON Web Token (JWT)

To decode a JSON Web Token (JWT), use Microsoft's jwt.ms tool. Values in the UI never leave your browser.

Example encoded JWT (shortened for display):

eyJ0eXAiOiJKV1QiLCJhbGciOiJSUzI1NiIsImtpZCI6Ilg1ZVhrNHh5b2pORnVtMWtsMll0djhkbE5QNC1j ... bQdHBHGcQQRbW7Wmo6SWYG4V_bU55Ug_PW4pLPr20tTS8Ct7_uwy9DWrzCMzpD-EiwT5IjXwlGX3IXVjHIlX50IVIydBoPQtadvT7saKo1G5Jmutgq41o-dmz6-yBMKV2_nXA25Q

Example JWT decoded by the tool for an app that authenticates against Azure AAD B2C:

{
  "typ": "JWT",
  "alg": "RS256",
  "kid": "X5eXk4xyojNFum1kl2Ytv8dlNP4-c57dO6QGTVBwaNk"
}.{
  "exp": 1610059429,
  "nbf": 1610055829,
  "ver": "1.0",
  "iss": "https://mysiteb2c.b2clogin.com/5cc15ea8-a296-4aa3-97e4-226dcc9ad298/v2.0/",
  "sub": "5ee963fb-24d6-4d72-a1b6-889c6e2c7438",
  "aud": "70bde375-fce3-4b82-984a-b247d823a03f",
  "nonce": "b2641f54-8dc4-42ca-97ea-7f12ff4af871",
  "iat": 1610055829,
  "auth_time": 1610055822,
  "idp": "idp.com",
  "tfp": "B2C_1_signupsignin"
}.[Signature]

Additional resources