add user data to subscription metadata

app/controllers/subscriptions_controller.rb

@@ -30,7 +30,8 @@ module DiscoursePatrons
 
         @subscription = ::Stripe::Subscription.create(
           customer: params[:customer],
-          items: [ { plan: params[:plan] } ]
+          items: [ { plan: params[:plan] } ],
+          metadata: { username_lower:  current_user.username_lower  },
         )
 
         group = plan_group(plan)

spec/requests/subscriptions_controller_spec.rb

@@ -24,7 +24,8 @@ module DiscoursePatrons
           ::Stripe::Plan.expects(:retrieve).returns(metadata: { group_name: 'awesome' })
           ::Stripe::Subscription.expects(:create).with(
             customer: 'cus_1234',
-            items: [ plan: 'plan_1234' ]
+            items: [ plan: 'plan_1234' ],
+            metadata: { username_lower: user.username_lower },
           )
           post "/patrons/subscriptions.json", params: { plan: 'plan_1234', customer: 'cus_1234' }
         end