* https://w3c.github.io/webappsec-referrer-policy/
* ('no-referrer', 'no-referrer-when-downgrade', 'same-origin',
* 'origin', 'strict-origin', 'origin-when-cross-origin',
* https://w3c.github.io/webappsec-referrer-policy/
* ('no-referrer', 'no-referrer-when-downgrade', 'same-origin',
* 'origin', 'strict-origin', 'origin-when-cross-origin',