Is it possible to put a password to a form

Idea being first line would request the password then the rest of the form would appear?

Yes it is possible. Just do not use the word/term 'Password' since the Phishing filter will confuse to the form that its a login form. The Phishing filter will block the form as it will appear to be against the Terms of Use.

Use 'code' or 'your code' or "id code' to be clear it is not a login password.

You can also use something similar to solution provided on this user guide:

Allow-Jotform-to-Be-Filled-out-Only-by-Those-with-a-Special-Link

Hope this help. Let us know how it goes.