Show smart proxy errors on unattended failure
If your proxy is has some error (like misconfigured sudoers, puppet not available, etc...) and you try to boot a host through unattended mode , the exception will not show up when you try to fetch the kickstart template. Instead, it will show something like No HTTP_REFERER was set in the request to this action, so redirect_to :back could not be called successfully.
The application controller should be aware of this situation and don't try to redirect to back in it, instead just render the error.
 an example of such error - ProxyAPI::ProxyException: ERF12-0104 [ProxyAPI::ProxyException]: Unable to set PuppetCA autosign for tonia-rippeon.lobatolan.home ([RestClient::NotAcceptable]: 406 Not Acceptable) for proxy https://centos7-devel.lobatolan.home:9090/puppet/ca