JotForm is a free online form builder which helps you create online forms without writing a single line of code. No sign-up required.
We believe that if one user has a question, there could be more users who may have the same question. This is why many of our support forum threads are public and available to be searched and viewed. If you’d like help immediately, feel free to search for a similar question, or submit your question or concern.
Are you referring to a membership function where your user can login to the form using the registered username and password?
If yes, then I'm sorry to inform you that this functionality is not available in JotForm. We don't have a membership feature. You can use JotForm though to have a registration or sign up form.
You can check MemberKit and verify if that is what you need.