Content Security Policy?

Interesting. It looks like there indeed can be a conflict with CSP: https://issues.chromium.org/issues/40903589

Please share how you’ve configured your Content-Security-Policy.

Note also that the script[type=speculationrules] tag is getting printed with wp_print_inline_script_tag(). So you would be able to inject a nonce attribute on that script tag via the wp_inline_script_attributes filter.

• This reply was modified 5 months, 3 weeks ago by Weston Ruter.

I just replicated this issue by enabling Strict CSP but not including a nonce attribute on the speculationrules script tag. So the key is to add the nonce attribute to that script tag as well.

This plugin which enables Strict CSP automatically adds it to the speculationrules script as well: https://gist.github.com/westonruter/c8b49406391a8d86a5864fb41a523ae9

So you can use PHP code like this:

add_filter(
	'wp_inline_script_attributes',
	static function ( $attributes ) {
		$attributes['nonce'] = my_csp_nonce();
		return $attributes;
	}
);

Where my_csp_nonce() is replaced with your logic to obtain the nonce.

Please share how you’ve configured your Content-Security-Policy.

We currently have no mention of script-src in it. I THINK that doing something like:
script-src ‘self’ ‘unsafe-inline’; should make it work.

Do you have a suggested method of testing whether or not this prefetching/prerendering is actually working as expected? Should I be able to watch the Network tab as I hover over links? Is there another method?

Chrome DevTools has a panel specifically for debugging Speculation Rules: https://developer.chrome.com/docs/devtools/application/debugging-speculation-rules

In video form: https://developer.chrome.com/blog/devtools-tips-31

Awesome – thank you so much. I’ll take a look at this in the days to come and report back.

Alternatively, you can add the 'inline-speculation-rules' directive value to your CSP, instead of adding a nonce. h/t @tunetheweb

Correction from @tunetheweb. The 'inline-speculation-rules' directive value wouldn’t work. It would only work for Speculation Rules added via scripting. So yeah, it seems the nonce is the best bet.