How to open the form to specific users

Also for judges, how to make sure it is marked by them and not others?

A workaround would be hiding them entire form under a form collapse, please check this guide: 
https://www.jotform.com/help/297-Show-or-Hide-multiple-fields-at-once-using-form-collapse-tool 

Makes sure not to label the field with the "Password" word, because our phishing detector system may suspend the form. Try using different labels such as "Access Key" or similar.

Let us know if you need more help.