Allow users to create logins that will pre-populate fields of a form

We are an auto glass replacement company. Insurance agents use an online form to submit customer data to us. The same agents use our form over and over and end up having to re-enter their own information like: Name, Agency Name, Email, Agency Phone, etc. I would like for insurance agents to have the ability to create a "login" with username and password that links to a profile for them. Then the form could pre-populate with their data (allowing them to alter or update anything that might have changed), as well as entering the information unique that the customer they are referring to us. Please see: [login to view URL] for how we currently do this.