There is this question that addresses "POSTing to an iframe using JavaScript".
My scenario:
I am not allowed to use JavaScript or any of its libraries. Only thing I can use is PHP and HTML.
Page1.php:
<form action="Page2.php"> <input type=".... > . . . </form>
Page2.php:
<iframe src="http://externalsite.com/post-to-this-address-thru-iframe"> </iframe>
This is always possible when JavaScript is used. Using PHP's post functions like curl also won't do. Is there really a source of light for me?