Add OIDC fixes, add prefered_username, add application-user claims

app/controllers/oidc_controller.rb

@@ -534,9 +534,6 @@ class OidcController < ApplicationController
       claims[:groups] = user.groups.pluck(:name)
     end
 
-    # Add admin claim if user is admin
-    claims[:admin] = true if user.admin?
-
     # Merge custom claims from groups
     user.groups.each do |group|
       claims.merge!(group.parsed_custom_claims)
@@ -545,6 +542,10 @@ class OidcController < ApplicationController
     # Merge custom claims from user (overrides group claims)
     claims.merge!(user.parsed_custom_claims)
 
+    # Merge app-specific custom claims (highest priority)
+    application = access_token.application
+    claims.merge!(application.custom_claims_for_user(user))
+
     render json: claims
   end