title: How to use IdentityServer4 with Custom password validation with ASP.NET Microsoft Identity
body: <p>I am working with IdentityServer4 and using ASP.NET Identity, and would like to do custom password validation so that I can add validation for password expiration (such as if password is older than 90 days then make the user change the password, etc...).</p>
  
  <p>I ran across the method <code>.AddPasswordValidator&lt;&gt;</code> when setting the <code>services.AddIdentity</code> in the <code>ConfigureServices()</code> method of the Startup.cs, but am unable to find any clear documentation on how to implement it.</p>
  
  <p>Can anyone help with implementation or point me toward some example code of something similar?  (Or possibly help with understanding where / how I could implement some custom validation of users/passwords with IdentityServer4)? </p>