Customizer: Some error handling should be included, e.g. for cookie expiration

[ocean90]

You are customizing your theme and suddenly your cookies are expired, then the Customizer doesn't show any notice.

Changes via postMessage are still visible, but changes which need an iframe refresh aren't visible, since the server response is an error. It includes the HTML page for the Cheatin’ uh? message.

Another problem is, when you try to save the changes. You can click the button, you will see the spinning image and the button text is changing to Saved. But it doesn't save anything, because the server response is an error again. Now a raw Cheatin’ uh? message.

Seems like we need an extra wp_die handler for the Customizer.

20876.patch​ is a first approach to handle error messages for iframe reloads.

The PHP should be considered done here. koopersmith is working on the JS.

I might step in and help with refreshing second-tick nonces if we find that to be something we should address.

Latest patch adds JS to handle logins in the customizer (so you don't lose state), and handles cheaters.

Does not handle nonce refreshing.

Updated to handle conflicts with trunk, add IFRAME_REQUEST to customize.php (which prevents is_admin_bar_showing() from returning true, amongst other things), and moves the wp-login customize enqueue_script to the necessary step. Also gets rid of debug cruft.

20876.diff​ implements a nonce check for ajax previews, via the customize-preview-$stylesheet nonce. (Saves are already implemented with customize-controls-$stylesheet.) The preview nonce is then check for its nonce tick, and if in the second half of its life, fresh nonces are returned for both customize-controls and customize-preview. koopersmith will be cleaning up the JS and ensuring that, if new nonces are returned, they begin to get used for future previews and saves.

Adds nonce updating.

20876.2.diff​ looks good. Ready for final review.

Tested all three states, works fine for me.

In [21031]:

Customizer: Gravefully handle cookie expipration. Prompt for log in in the preview. Props ocean90, koopersmith, nacin. fixes #20876

In [21135]:

Refresh nonces in the customizer. props koopersmith. see #20876.

In [21136]:

Refresh nonces in the customizer. props koopersmith. see #20876 for 3.4.