title: Python click option with a prompt AND default hidden
body: <p>The snippet below prompts for the user and password, and defaults to env variables.</p>
  
  <p>Now while the password input is well hidden while typing, I'd like also to have the default between brackets hidden as well, so far if I enter this, the password default is in clear <strong>1234</strong>:</p>
  
  <pre><code>➜  export PASSWORD=1234
  ➜  python test.py
  ➜  User [myuser]: you can see here
  ➜  Password [1234]: 
  user you can see here
  password you cant see
  
  
  import os
  import click
  
  @click.command()
  @click.option('--user', prompt=True, default=lambda: os.environ.get('USER', ''))
  @click.option('--password', prompt=True, default=lambda: os.environ.get('PASSWORD', ''), hide_input=True)
  def test(user, password):
      print('user {}'.format(user))
      print('password {}'.format(password))
      print(password)
  
  
  if __name__ == '__main__':
      test()
  </code></pre>