title: Authentication failed pysftp with private key
body: <p>Using the Pysftp library to sftp to a server, I am getting Authentication failed when attempting to connect.</p>
  <p>However using the same credentials in filezilla I am able to connect.</p>
  <pre><code>from pysftp import CnOpts, Connection
  from paramiko import RSAKey
  import io
  
  private_key_text = '''
  -----BEGIN OPENSSH PRIVATE KEY-----
     key removed...
  -----END OPENSSH PRIVATE KEY-----
  '''
  
      passphrase = 'my_passphrase'
      private_key = RSAKey.from_private_key(io.StringIO(private_key_text), password=passphrase)
      host = 'host_address'
      username = 'username'
      cnopts = CnOpts()
      target_dir = '/home'
      cnopts.hostkeys = None
      with Connection(host=host, username=username, private_key=private_key, private_key_pass=passphrase,
                      cnopts=cnopts, default_path=target_dir) as sftp:
          print(f'Successfully connected to remote SFTP server [{host}]')
      
  </code></pre>