Multiple Identities in ASP.NET Core 2.0

Question

I am migrating an ASP.NET Core 1.0 application to ASP.NET Core 2.0.

In my startup I am configuring two identities:

services.AddIdentity<IdentityUser, IdentityRole>(configureIdentity)
   .AddDefaultTokenProviders()
   .AddUserStore<IdentityUserStore<IdentityUser>>()
   .AddRoleStore<IdentityRoleStore<IdentityRole>>();

services.AddIdentity<Customer, CustomerRole>(configureIdentity)
   .AddDefaultTokenProviders()
   .AddErrorDescriber<CustomerIdentityErrorDescriber>()
   .AddUserStore<CustomerStore<Customer>>()
   .AddRoleStore<CustomerRoleStore<CustomerRole>>();

This worked fine in ASP.NET Core 1.0 but fails with the error: System.InvalidOperationException: 'Scheme already exists: Identity.Application' in ASP.NET Core 2.0.

In ASP.NET Core 2.0, if I remove one of the calls to AddIdentity the error goes away. How do I migrate my code so that I can use two different types of identity user and role in my application? Or did I just make a fundamental error in understanding how things work back when I wrote this in ASP.NET Core 1.0?

Answer 1

After looking through the ASP.NET Core source code on github, a second identity could be added using this extension method:

using Microsoft.AspNetCore.Identity;
using Microsoft.Extensions.DependencyInjection;
using Microsoft.Extensions.DependencyInjection.Extensions;
using System;
using System.Collections.Generic;
using System.Text;

namespace Whatever
{
    public static class IdentityExtensions
    {
        public static IdentityBuilder AddSecondIdentity<TUser, TRole>(
            this IServiceCollection services)
            where TUser : class
            where TRole : class
        {
            services.TryAddScoped<IUserValidator<TUser>, UserValidator<TUser>>();
            services.TryAddScoped<IPasswordValidator<TUser>, PasswordValidator<TUser>>();
            services.TryAddScoped<IPasswordHasher<TUser>, PasswordHasher<TUser>>();
            services.TryAddScoped<IRoleValidator<TRole>, RoleValidator<TRole>>();
            services.TryAddScoped<ISecurityStampValidator, SecurityStampValidator<TUser>>();
            services.TryAddScoped<IUserClaimsPrincipalFactory<TUser>, UserClaimsPrincipalFactory<TUser, TRole>>();
            services.TryAddScoped<UserManager<TUser>, AspNetUserManager<TUser>>();
            services.TryAddScoped<SignInManager<TUser>, SignInManager<TUser>>();
            services.TryAddScoped<RoleManager<TRole>, AspNetRoleManager<TRole>>();

            return new IdentityBuilder(typeof(TUser), typeof(TRole), services);
        }
    }
}

Answer 2

Asp.net Core 2.2 provides a built-in method for that purpose.

AddIdentityCore<TUser>

How to use it:

services.AddIdentity<IdentityUser, IdentityRole>(configureIdentity)
   .AddDefaultTokenProviders()
   .AddUserStore<IdentityUserStore<IdentityUser>>()
   .AddRoleStore<IdentityRoleStore<IdentityRole>>();

services.AddIdentityCore<Customer>(configureIdentity)
   .AddDefaultTokenProviders()
   .AddErrorDescriber<CustomerIdentityErrorDescriber>()
   .AddUserStore<CustomerStore<Customer>>()
   .AddRoleStore<CustomerRoleStore<CustomerRole>>();

services.AddScoped<RoleManager<Customer>>();

In fact, read the implementation of this method from asp.net core 2.2 github repo

    /// <summary>
    /// Adds and configures the identity system for the specified User type. Role services are not added by default 
    /// but can be added with <see cref="IdentityBuilder.AddRoles{TRole}"/>.
    /// </summary>
    /// <typeparam name="TUser">The type representing a User in the system.</typeparam>
    /// <param name="services">The services available in the application.</param>
    /// <param name="setupAction">An action to configure the <see cref="IdentityOptions"/>.</param>
    /// <returns>An <see cref="IdentityBuilder"/> for creating and configuring the identity system.</returns>
    public static IdentityBuilder AddIdentityCore<TUser>(this IServiceCollection services, Action<IdentityOptions> setupAction)
        where TUser : class
    {
        // Services identity depends on
        services.AddOptions().AddLogging();

        // Services used by identity
        services.TryAddScoped<IUserValidator<TUser>, UserValidator<TUser>>();
        services.TryAddScoped<IPasswordValidator<TUser>, PasswordValidator<TUser>>();
        services.TryAddScoped<IPasswordHasher<TUser>, PasswordHasher<TUser>>();
        services.TryAddScoped<ILookupNormalizer, UpperInvariantLookupNormalizer>();
        services.TryAddScoped<IUserConfirmation<TUser>, DefaultUserConfirmation<TUser>>();
        // No interface for the error describer so we can add errors without rev'ing the interface
        services.TryAddScoped<IdentityErrorDescriber>();
        services.TryAddScoped<IUserClaimsPrincipalFactory<TUser>, UserClaimsPrincipalFactory<TUser>>();
        services.TryAddScoped<UserManager<TUser>>();

        if (setupAction != null)
        {
            services.Configure(setupAction);
        }

        return new IdentityBuilder(typeof(TUser), services);
    }

Answer 3

Thank you very much for your answer keith. This saved me a lot of time! One small improvement: I had to configure some options (IdentityOptions) in my case. Like for example: Password Complexity Rules.

I therefore included the registering of the Action setupAction. (This is the same way Microsoft does it within the AddIdentity inside IdentityServiceCollectionExtension)

public static class IdentityExtensions
{
    public static IdentityBuilder AddSecondIdentity<TUser, TRole>(
        this IServiceCollection services, Action<IdentityOptions> setupAction)
        where TUser : class
        where TRole : class
    {
        services.TryAddScoped<IUserValidator<TUser>, UserValidator<TUser>>();
        services.TryAddScoped<IPasswordValidator<TUser>, PasswordValidator<TUser>>();
        services.TryAddScoped<IPasswordHasher<TUser>, PasswordHasher<TUser>>();
        services.TryAddScoped<IRoleValidator<TRole>, RoleValidator<TRole>>();
        services.TryAddScoped<ISecurityStampValidator, SecurityStampValidator<TUser>>();
        services.TryAddScoped<IUserClaimsPrincipalFactory<TUser>, UserClaimsPrincipalFactory<TUser, TRole>>();
        services.TryAddScoped<UserManager<TUser>, AspNetUserManager<TUser>>();
        services.TryAddScoped<SignInManager<TUser>, SignInManager<TUser>>();
        services.TryAddScoped<RoleManager<TRole>, AspNetRoleManager<TRole>>();

        if (setupAction != null)
            services.Configure(setupAction);

        return new IdentityBuilder(typeof(TUser), typeof(TRole), services);
    }
}