input: Write a python function to read and update login credentials from a config file using configparser.
  assert read_and_update_config('config.ini', 'login', 'name', 'password') == ('new_name', 'new_password')
  assert read_and_update_config('config.ini', 'login', 'name', 'password') == ('another_name', 'another_password')
output: import configparser
  
  def read_and_update_config(file_path, section, username_key, password_key):
      config = configparser.ConfigParser()
      config.read(file_path)
      
      # Read the current credentials
      current_username = config.get(section, username_key)
      current_password = config.get(section, password_key)
      
      # Generate new credentials (for demonstration purposes, we'll just append '_new')
      new_username = current_username + '_new'
      new_password = current_password + '_new'
      
      # Update the config with new credentials
      config.set(section, username_key, new_username)
      config.set(section, password_key, new_password)
      
      # Write the updated config back to the file
      with open(file_path, 'w') as configfile:
          config.write(configfile)
      
      return new_username, new_password