How to use Asp.Net Core Identity in Multi-Tenant environment

Question

I have a working Asp.Net Core application with default Identity handling. Now I want to use it for multi domains. I extended ApplicationUser with DomainId. How can I handle

Answer 1

Finally I figured it out. So first, I have to set user email to not unique. Sidenote: I'm using email for UserName also, I don't like to ask UserName from users:

services.Configure(options =>
{
    options.User.RequireUniqueEmail = false;
});

When a new user register himself, I'm merging current Domain Id to UserName, this helps users to register with same Email / UserName into the system through totally different domains.

Then I had to create my custom UserManager, where I'm overriding FindByEmail:

using Microsoft.AspNetCore.Identity;
using Microsoft.Extensions.Logging;
using Microsoft.Extensions.Options;
using MultiShop.Core.Repositories.User;
using MultiShop.Core.Tenant;
using System;
using System.Collections.Generic;
using System.Linq;
using System.Threading.Tasks;

namespace Test
{
    public class MyShopUserManager : UserManager, IDisposable where TUser : class
{
    private readonly ITenantService tenantService;
    private readonly IUserRepository userRepository;

    public MyUserManager(IUserStore store, IOptions optionsAccessor,
        IPasswordHasher passwordHasher, IEnumerable> userValidators,
        IEnumerable> passwordValidators, ILookupNormalizer keyNormalizer,
        IdentityErrorDescriber errors, IServiceProvider services, ILogger> logger,
        ITenantService tenantService, IUserRepository userRepository)
        : base(store, optionsAccessor, passwordHasher, userValidators, passwordValidators, keyNormalizer, errors, services, logger)
    {
        this.tenantService = tenantService;
        this.userRepository = userRepository;
    }

    public override async Task FindByEmailAsync(string email)
    {
        ThrowIfDisposed();
        if (email == null)
        {
            throw new ArgumentNullException(nameof(email));
        }

        var users = (await userRepository.GetAllAsync()).Where(u => u.Email == email);

        if (users == null)
        {
            return null;
        }

        if (users.Count() == 1)
        {
            return await Store.FindByIdAsync(users.First().Id.ToString(), CancellationToken);
        }

        var currentDomain = tenantService.GetCurrentDomainAsync().Result;
        var user = users.SingleOrDefault(u => u.DomainId == currentDomain.Id);

        if (user == null)
        {
            return null;
        }

        return await Store.FindByIdAsync(user.Id.ToString(), CancellationToken);
    }
}
}

Be careful, because of multi-domains and generated UserNames, you should use userManager.FindByEmailAsync, instead of FindByNameAsync.

I had to create custom SignInManager for handling multi-domain users:

using Microsoft.AspNetCore.Authentication;
using Microsoft.AspNetCore.Http;
using Microsoft.AspNetCore.Identity;
using Microsoft.Extensions.Logging;
using Microsoft.Extensions.Options;
using MultiShop.Core.Tenant;
using MultiShop.Data.Entities;
using System.Threading.Tasks;

namespace Test
{
public class MySignInManager : SignInManager

{
    private readonly ITenantService tenantService;

    public MySignInManager(UserManager userManager, IHttpContextAccessor contextAccessor,
        IUserClaimsPrincipalFactory claimsFactory, IOptions optionsAccessor,
        ILogger> logger, IAuthenticationSchemeProvider schemes,
        ITenantService tenantService)
        : base(userManager, contextAccessor, claimsFactory, optionsAccessor, logger, schemes)
    {
        this.tenantService = tenantService;
    }

    public override async Task PasswordSignInAsync(string userName, string password, bool isPersistent, bool lockoutOnFailure)
    {
        var currentDomain = await tenantService.GetCurrentDomainAsync();
        return await base.PasswordSignInAsync($"{userName}{currentDomain.Id}", password, isPersistent, lockoutOnFailure);
    }
}
}

Finally I have to register my custom managers into Asp.Net Core Identity DI:

services
   .AddIdentity()
   .AddEntityFrameworkStores()
   .AddDefaultTokenProviders()
   //my custom managers for domain segmented users
   .AddUserManager>()
   .AddSignInManager();

That's it!