Get user id in ASP.NET Core 2

You need to inject dependency in the controller like shown below:

[Authorize]
public class AccountController: Controller
{
private readonly UserManager<IdentityUser> _userManager;

    public AccountController(UserManager<IdentityUser> userManager) 
    {
        _userManager = userManager;
    }
}

Now, you can use below code anywhere inside that controller to get user details.

var user = await _userManager.FindByEmailAsync(model.EmailID);

Now, You can use user.Id to get userId.

The old method of User.Identity.GetUserId() no longer exists, but the id is available as a claim on your principal, i.e. User. There's a number of ways you can get to it:

1. The first and easiest is just pull out the claim:

   var userId = User.FindFirstValue(ClaimTypes.NameIdentifier);
   

2. If you already have an instance of UserManager<TUser> (or want to inject one), then you can use the GetUserId() method on that:

   var userId = _userManager.GetUserId(User);
   

3. Finally, if you want the old way back, it's as simple as adding an extension to ClaimsPrincipal and utilize the first method above:

   public static class ClaimsPrincipalExtensions
   {
       public static string GetUserId(this ClaimsPrincipal principal) =>
           principal.FindFirstValue(ClaimTypes.NameIdentifier);
   }