@Gargron On #Friendica we use a local proxy feature for OEmbed, so that it's on the same domain as the node.

Ex: https://friendica.mrpetovan.com/oembed/aHR0cHM6Ly90d2l0dGVyLmNvbS9ldmVyeWRheWxvdWllL3N0YXR1cy85Mzg4MDc1MzA1MTU0MTUwNDA=

Where aHR0cHM6Ly90d2l0dGVyLmNvbS9ldmVyeWRheWxvdWllL3N0YXR1cy85Mzg4MDc1MzA1MTU0MTUwNDA= simply is the base64 encode of the target URL.