Hi @anon6606375, welcome to the Asana Community Forum and thanks for sharing your feedback with us! As it stands, it’s currently not possible to enable reCaptcha or a similar feature to form links. I’ve gone ahead and moved your thread to the #productfeedback category to allow other users to upvote. Hopefully this is something we can implement in the future.
You can also vote for [Forms] Ability to manage Forms permissions!