What is JotForm?
JotForm is a free online form builder which helps you create online forms without writing a single line of code. No sign-up required.
At JotForm, we want to make sure that you’re getting the online form builder help that you need. Our friendly customer support team is available 24/7.
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.
Your forms are already protected since they are within your JotForm account. If you do not share your JotForm account, then, only you should be able to access your forms -- making them protected by your JotForm account username/password.
But if you meant password protecting your live form in your website, then, you can just setup a login page in your website before users can reach/access the embedded form on the website.
BUT again, if your intention was to add a username/password input in your form like a login form -- then, this option is not available in the form. The form are NOT useable as a login type of form, as this could be considered as a potential phishing procedure that will warrant disablement or suspension of your JotForm forms.
I hope I am able to answer your question. Inform us if further clarification is needed.