So, while combing through yet another occult mass upload someone linked me, I came across Koetting’s eBook, Rape of the Archangels. In it is given an account of a mystic named Tilopa who rapes the Queen of the Dakinis and, by so doing, gains many siddhis (spiritual powers).
I have been unable to find any literary sources corroborating this story. Can anyone tell me what texts I should be looking for?