Glue won't hold.
My favorite method involves trapping the pinback under a "bandaid" of clay; essentially cut a strip that fits over the pin and stretches out on either side on the back of the piece. Use a dab of liquid clay or bake-and-bond to enhance the bond. Impress neatly with texture to help produce a finished look; you can even "sign" your work there with a small stamp or carve your initials with a needle tool.
You can also put a larger sheet over the whole back of your piece, cutting tiny holes where the arms of the pinback come through the piece; I do this when I plan ahead far enough. This way the finding vanishes into the piece almost completely. And it is stronger. I do that most often with hairclips.
In either case, the pinback is mounted to an already-baked front, and then baked a second time to cure the backing.