title: IdentityServer4 Add Tenant Claim after Authentication
body: <p>I have a multi-tenant scenario in which one email can be associated with multiple tenants.</p>
  
  <p>I've thus configured a custom <code>AccountChooserResponseGenerator</code> that inherits from the built-in <code>AuthorizeInteractionResponseGenerator</code> class.</p>
  
  <p>After the user authenticates, the UI correctly diverts the user to an Account Chooser view, which lists the tenants the email address is associated with.  The idea being that the user must now select the Tenant he/she wants to log in to, and then get redirected to that Tenant's URI.</p>
  
  <p>My problem though is that I can't figure out how, after selecting a Tenant, I can add that Tenant Id as a Claim to the token that gets passed to the app from IdentityServer (multiple tenants could share the same URL so I need something in the token to know which Tenant has context).</p>
  
  <p>So in the <code>AccountChooserController.TenantSelected(long tenantId)</code> method, I'm expecting to be able to add this <code>tenantId</code> to the User Claims, but it does not seem like this is supported.</p>
  
  <p>Please advise if this is possible, and how?</p>