Can't access WordPress Dashboard in an iframe
Here is a better solution that won't break when you update Wordpress:
remove_action( 'login_init', 'send_frame_options_header' );remove_action( 'admin_init', 'send_frame_options_header' );Here's another solution if you're using Apache. Throw this in your .htaccess:
<IfModule mod_headers.c> Header unset X-Frame-Options Header always unset X-Frame-Options</IfModule>
According to this, in WordPress Answers, Receiving “This content cannot be displayed in a frame” error on login page, WordPress sends a special header
X-Frame-Options: SAMEORIGINthat prevents clickjacking. And hence, embedding the admin as an iframe.
It is possible to eliminate this header removing a couple of actions from wp-includes/default-filters.php, but at your own risk.
Someone might register a domain with a very similar name, embed your login as background iframe and log the login credentials when you try to type them in.
Please, read the full Q&A at WPSE.