code: def install_key_data(self, keydata, target):
          
  
          target.seek(0)
          contents = target.read()
          ssh_opts = 'no-port-forwarding'
          if keydata in contents:
              raise InstallError('key data already in file - refusing '
                                 'to double-install.\n')
          command = '%s --run' % self.authprogs_binary
          if self.logfile:
              command += ' --logfile=%s' % self.logfile
          if self.keyname:
              command += ' --keyname=%s' % self.keyname
  
          target.write('command="%(command)s",%(ssh_opts)s %(keydata)s\n' %
                       {'command': command,
                        'keydata': keydata,
                        'ssh_opts': ssh_opts})
docs: Install the key data into the open file.