track where ga signups come from

app/create.rb

@@ -58,7 +58,8 @@ post '/create' do
     email: params[:email],
     new_tags_string: params[:new_tags_string],
     is_education: params[:is_education] == 'true' ? true : false,
-    ip: request.ip
+    ip: request.ip,
+    ga_adgroupid: session[:ga_adgroupid]
   )
 
   if education_whitelisted?

app/index.rb

@@ -1,4 +1,8 @@
 get '/?' do
+  if params[:_ga_adgroupid]
+    session[:ga_adgroupid] = params[:_ga_adgroupid]
+  end
+
   if current_site
     require_login