validate account config keys

app/controllers/account_configs_controller.rb

@@ -11,6 +11,8 @@ class AccountConfigsController < ApplicationController
     AccountConfig::ESIGNING_PREFERENCE_KEY
   ].freeze
 
+  InvalidKey = Class.new(StandardError)
+
   def create
     @account_config.update!(account_config_params)
 
@@ -20,7 +22,7 @@ class AccountConfigsController < ApplicationController
   private
 
   def load_account_config
-    return head :not_found unless ALLOWED_KEYS.include?(account_config_params[:key])
+    raise InvalidKey unless ALLOWED_KEYS.include?(account_config_params[:key])
 
     @account_config =
       AccountConfig.find_or_initialize_by(account: current_account, key: account_config_params[:key])