This is the custome user factory class for using with role based authorization in Blazor Apps got this class code from the book "Blazor in action" by Chris Sainty

CustomUserFactory.cs

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

namespace {Enter your namespace name here}
{
    public class CustomUserFactory<TAccount> : AccountClaimsPrincipalFactory<RemoteUserAccount>
    {
        public CustomUserFactory(IAccessTokenProviderAccessor accessor) : base(accessor) { }
       
        public override async ValueTask<ClaimsPrincipal> CreateUserAsync(RemoteUserAccount account,RemoteAuthenticationUserOptions options)
        {
            var initialUser = await base.CreateUserAsync(account, options);
            if (initialUser?.Identity?.IsAuthenticated ?? false)
            {
                var userIdentity = (ClaimsIdentity)initialUser.Identity;
                account.AdditionalProperties.TryGetValue(ClaimTypes.Role, out var roleClaimValue);
                if (roleClaimValue is not null && roleClaimValue is JsonElement element && element.ValueKind == JsonValueKind.Array)
                {
                    userIdentity.RemoveClaim(userIdentity.FindFirst(ClaimTypes.Role));
                    var claims = element.EnumerateArray()
                    .Select(x => new Claim(ClaimTypes.Role, x.ToString()));
                    userIdentity.AddClaims(claims);
                }
            }
            return initialUser ?? new ClaimsPrincipal();
        }
}
}

UserRoleFlow.js

//Code to set user role in Auth0 for blazorApp
exports.onExecutePostLogin = async (event, api) => {
  const roleClaim = 'http://schemas.microsoft.com/ws/2008/06/identity/claims/role';
  
  if (event.authorization) {
    api.idToken.setCustomClaim(roleClaim, event.authorization.roles);
  }
};