I read about this for the first time in "La ultima bruja" (2017), a book about witches. In this book, there's a chapter in which a girl has to have sexual relationships with a Wolf God so He grants her power to become a witch.
I've seen this idea represented in the shows "The Magicians" and "American Gods" as well. In the first show, two characters get extra powers by drinking a God's "seed" and by having sex with another one.
Assuming that these works are based on the same "origin" or reference, is there some kind of "official" reference for this, some kind of "de facto" example in which a god/goddess grants power to another mortal or being by having sex with them?