That's almost exactly how we (optionally, of course) import your SSH key from Github at Userify.. (well, technically we're using Python requests, not curl, but otherwise exactly the same).

The beauty of doing it this way (writing authorized_keys) is that the accounts are completely independent from a third-party auth service. (ok, I guess technically that's what we are, but we're only managing the public keys, and not directly authenticating through a remote server like a directory or database.) SSH has a beautiful design.