Unable to resolve service for type 'Microsoft.AspNetCore.Identity.UserManager` while attempting to activate 'AuthController'

You need to use the same user data model in SignInManager, UserManager and services.AddIdentity. Same principal is true if you are using your own custom application role model class.

So, change

services.AddIdentity<IdentityUser, IdentityRole>(options =>
    {
        options.User.RequireUniqueEmail = false;
    })
    .AddEntityFrameworkStores<Providers.Database.EFProvider.DataContext>()
    .AddDefaultTokenProviders();

to

services.AddIdentity<Automobile.Models.Account, IdentityRole>(options =>
    {
        options.User.RequireUniqueEmail = false;
    })
    .AddEntityFrameworkStores<Providers.Database.EFProvider.DataContext>()
    .AddDefaultTokenProviders();

Just to be clear about the answer:

If you use the class ApplicationUser in startup.cs: services.AddIdentity<ApplicationUser, IdentityRole>()

then you must use the same class in your controller when injecting it:

public AccountController(UserManager<ApplicationUser> userManager)

If you use some other class such as:

public AccountController(UserManager<IdentityUser> userManager)

then you will get this error:

InvalidOperationException: Unable to resolve service for type 'Microsoft.AspNetCore.Identity.UserManager`1[IdentityUser]'

because you used ApplicationUser in startup, not IdentityUser so this type is not registered with the injection system.

This is a bit unrelated to the original post but since Google brings you here... if you are getting this error and are using:

services.AddIdentityCore<YourAppUser>()

Then you will need to manually register the stuff that AddIdentity does, which can be found here: https://github.com/aspnet/Identity/blob/feedcb5c53444f716ef5121d3add56e11c7b71e5/src/Identity/IdentityServiceCollectionExtensions.cs#L79

        services.AddHttpContextAccessor();
        // Identity services
        services.TryAddScoped<IUserValidator<TUser>, UserValidator<TUser>>();
        services.TryAddScoped<IPasswordValidator<TUser>, PasswordValidator<TUser>>();
        services.TryAddScoped<IPasswordHasher<TUser>, PasswordHasher<TUser>>();
        services.TryAddScoped<ILookupNormalizer, UpperInvariantLookupNormalizer>();
        services.TryAddScoped<IRoleValidator<TRole>, RoleValidator<TRole>>();
        // No interface for the error describer so we can add errors without rev'ing the interface
        services.TryAddScoped<IdentityErrorDescriber>();
        services.TryAddScoped<ISecurityStampValidator, SecurityStampValidator<TUser>>();
        services.TryAddScoped<ITwoFactorSecurityStampValidator, TwoFactorSecurityStampValidator<TUser>>();
        services.TryAddScoped<IUserClaimsPrincipalFactory<TUser>, UserClaimsPrincipalFactory<TUser, TRole>>();
        services.TryAddScoped<UserManager<TUser>>();
        services.TryAddScoped<SignInManager<TUser>>();
        services.TryAddScoped<RoleManager<TRole>>();

You'll need to replace TUser and TRole with your implementations of those, or the default IdentityUser, IdentityRole

You can set IdentityUser and IdentityRole in ConfigureServices inside Startup class individually as shown below:

services.AddDefaultIdentity<IdentityUser>()
    .AddRoles<IdentityRole>()
    .AddEntityFrameworkStores<ApplicationDbContext>();

OR

you can configure directly into AddIdentity:

services.AddIdentity<IdentityUser, IdentityRole>()
        .AddEntityFrameworkStores<ApplicationDbContext>();

don't forget to add role manager in ConfigureServices

services.AddDefaultIdentity<IdentityUser>()
    .AddRoles<IdentityRole>() // <--------
    .AddDefaultUI(UIFramework.Bootstrap4)
    .AddEntityFrameworkStores<ApplicationDbContext>();

If you're using "IdentityServer" so IdentityServer authenticates the user and authorizes the client.By default, IdentityServer is actually not about user management. But there is some support for asp.net Identity

So you need add :

services.AddIdentityServer()
    .AddAspNetIdentity<ApplicationUser>();

You need to update your Statup.cs class with below

services.AddIdentity() .AddEntityFrameworkStores();

Here : ApplicationUser is my custom model class.