Return username and password for the KM3NeT WebDB.

def db_credentials(self):
        """Return username and password for the KM3NeT WebDB."""
        try:
            username = self.config.get('DB', 'username')
            password = self.config.get('DB', 'password')
        except Error:
            username = input("Please enter your KM3NeT DB username: ")
            password = getpass.getpass("Password: ")
        return username, password