title: Implement email confirmation with digit code
body: <p>I want to implement email confirmation with digit code for my .net core web app.
  I make use of the GenerateEmailConfirmationTokenAsync from the UserManager class, but it returns a token instead of a digit code. I think I should create a custom implementation using the IUserTokenProvider interface, but I cant find any example. </p>
  
  <p>How can I implement this using the IUserTokenProvider?</p>