Yes. The app is already designed with password protection. When you signed up you provided an email and password. Normally the app doesn't ask you to login as it creates a session for you.
Just follow these steps to require a password to open the app
When complete with your session open the Setting page.
Click the button Logout at the bottom. This will log you out of the system
The next time you open the app, click on Login button at the bottom.