Set host for RS auth url

With X-Forwarded-Host set on the proxied request, Rails uses that host
for URLs. But we need it to be the accounts domain.

app/controllers/webfinger_controller.rb

@@ -74,7 +74,7 @@ class WebfingerController < WellKnownController
   end
 
   def remotestorage_link
-    auth_url = new_rs_oauth_url(@username)
+    auth_url = new_rs_oauth_url(@username, host: Setting.accounts_domain)
     storage_url = "#{Setting.rs_storage_url}/#{@username}"
 
     {