using System.Web.Security;
....
// NOTE: This is a static method .. which makes things easier to use.
MembershipUser user = Membership.GetUser(User.Identity.Name);
if (user == null)
{
throw new InvalidOperationException("User [" +
User.Identity.Name + " ] not found.");
}
// Do whatever u want with the unique identifier.
Guid guid = (Guid)user.ProviderUserKey;
using Microsoft.AspNet.Identity;
using Microsoft.AspNet.Identity.EntityFramework;
using Microsoft.Owin.Security;*
public myFunc()
{
.....
// Code which will give you user ID is
var tmp = User.Identity.GetUserId();
}