code: def _get_key_info(self):
          
          if self._key_info_cache is not None:
              return self._key_info_cache
  
          errors = []
  
          # First try the agent.
          try:
              key_info = agent_key_info_from_key_id(self.key_id)
          except MantaError:
              _, ex, _ = sys.exc_info()
              errors.append(ex)
          else:
              self._key_info_cache = key_info
              return self._key_info_cache
  
          # Try loading from "~/.ssh/*".
          try:
              key_info = ssh_key_info_from_key_data(self.key_id)
          except MantaError:
              _, ex, _ = sys.exc_info()
              errors.append(ex)
          else:
              self._key_info_cache = key_info
              return self._key_info_cache
  
          raise MantaError("could not find key info for signing: %s" %
                           "; ".join(map(str, errors)))
docs: Get key info appropriate for signing: either from the ssh agent
          or from a private key.