I\'m using the jQuery ajaxForms plugin to make an ajax submit to my CakePHP app.
Cake\'s RequestHandler detects ajax requests by looking at the \"X-Requested-With\
@Nicky De Maeyer's answer to his own question
Actually you don't need to do this yourself (appending a hidden input field).
AFAIK you can just pass such data to ajaxForms plugin in the options object
$('#myForm1').ajaxForm({data:{"X_REQUESTED_WITH":"XMLHttpRequest"}});
Should automagically (in the hidden iframe file upload case) append such an input to your form on submission