Steps to Reproduce:
Go to https://a.tiles.wmflabs.org/osm-no-labels/16/10309/22655.png in a web browser (Chrome, Firefox, etc.)
An SSL certificate warning (SSL_ERROR_BAD_CERT_DOMAIN) is received. If I want to go through to the tile image, I need to add a whitelist rule to my browser.
I'm able to load the tile over https without having to add a whitelist rule.