Trebach on Nostr: npub1zylk3…ct54n might be an option, though you'd probably have to add a session id ...

npub1zylk3x2cvl79r854gtnqjvh7cjns6zzynvf39llvfvh6gl89cgvslct54n (npub1zyl…t54n) https://mcaptcha.org/ might be an option, though you'd probably have to add a session id in there to make sure the user didn't have multiple windows open all on the signup page to try to parallelize creating accounts