You are developing a WebAssembly authentication app and trying to implement Roles based access control. You are getting a similar error like…

  • You are not authorized to access this resource.
  • Microsoft.AspNetCore.Authorization.DefaultAuthorizationService[2]Authorization failed. These requirements were not met: RolesAuthorizationRequirement:User.IsInRole must be true for one of the following roles: (ROLE_NAME)

The WebAssembly Authentication stack appears to cast the roles claim into a single string. We need this User Factory to modify its behavior so that each role has its own unique value.

Create the Custom User Factory

First, create a custom User Factory (CustomUserFactory.cs)…

using Microsoft.AspNetCore.Components.WebAssembly.Authentication;
using Microsoft.AspNetCore.Components.WebAssembly.Authentication.Internal;
using System.Security.Claims;
using System.Text.Json;

public class CustomUserFactory : AccountClaimsPrincipalFactory<RemoteUserAccount>
    public CustomUserFactory(IAccessTokenProviderAccessor accessor)
        : base(accessor)

    public async override ValueTask<ClaimsPrincipal> CreateUserAsync(
        RemoteUserAccount account,
        RemoteAuthenticationUserOptions options)
        var user = await base.CreateUserAsync(account, options);
        var claimsIdentity = (ClaimsIdentity?)user.Identity;

        if (account != null && claimsIdentity != null)
            MapArrayClaimsToMultipleSeparateClaims(account, claimsIdentity);

        return user;

    private void MapArrayClaimsToMultipleSeparateClaims(RemoteUserAccount account, ClaimsIdentity claimsIdentity)
        foreach (var prop in account.AdditionalProperties)
            var key = prop.Key;
            var value = prop.Value;
            if (value != null && (value is JsonElement element && element.ValueKind == JsonValueKind.Array))
                // Remove the Roles claim with an array value and create a separate one for each role.
                var claims = element.EnumerateArray().Select(x => new Claim(prop.Key, x.ToString()));

Add the roles mapping and CustomUserFactory to your authentication Middleware

If you’re using AddOidcAuthentication…

builder.Services.AddOidcAuthentication(options =>
    builder.Configuration.Bind("AzureAd", options.ProviderOptions);
    options.ProviderOptions.AdditionalProviderParameters.Add("domain_hint", "");
    options.UserOptions.RoleClaim = "roles";
    options.ProviderOptions.ResponseType = "code";

If you’re using AddMsalAuthentication…

builder.Services.AddMsalAuthentication(options =>
    builder.Configuration.Bind("AzureAd", options.ProviderOptions.Authentication);
    options.UserOptions.RoleClaim = "roles";

Protect your page

Now you can add the Authorize attribute to your blazor pages…

@attribute [Authorize(Roles="access_as_user")]

More Information

To learn more about WebAssembly Authentication…

Sample that has this solution implemented…

Don’t forget to add App Roles to your app registration, add your user to the app role, and configure your application to use the app role you have created.

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