code: def load_certificate(self, value):
          
          if isinstance(value, Message):
              constructor = "from_message"
          elif os.path.isfile(value):
              constructor = "from_file"
          else:
              constructor = "from_string"
          blob = getattr(PublicBlob, constructor)(value)
          if not blob.key_type.startswith(self.get_name()):
              err = "PublicBlob type {} incompatible with key type {}"
              raise ValueError(err.format(blob.key_type, self.get_name()))
          self.public_blob = blob
docs: Supplement the private key contents with data loaded from an OpenSSH
          public key (``.pub``) or certificate (``-cert.pub``) file, a string
          containing such a file, or a `.Message` object.
  
          The .pub contents adds no real value, since the private key
          file includes sufficient information to derive the public
          key info. For certificates, however, this can be used on
          the client side to offer authentication requests to the server
          based on certificate instead of raw public key.
  
          See:
          https://github.com/openssh/openssh-portable/blob/master/PROTOCOL.certkeys
  
          Note: very little effort is made to validate the certificate contents,
          that is for the server to decide if it is good enough to authenticate
          successfully.