User Specific Authentication to REST API Data Source

Is it possible to let the users authenticate to the REST API source? I have built a report hard coding my credentials in, but it would be best if the users could connect using their own username/pwd combination. I have it set up as parameters but I don't see how to make PBI ask the user for these when they open it up?

Also - how do we keep those credentials secure within the app so that people aren't getting others' creds if they send copies of the file to them?