whole_func_string: function refresh(callback) {
      var self = this;
      if (!callback) callback = function(err) { if (err) throw err; };
  
      self.metadataService.loadCredentials(function (err, creds) {
        if (!err) {
          self.expired = false;
          self.metadata = creds;
          self.accessKeyId = creds.AccessKeyId;
          self.secretAccessKey = creds.SecretAccessKey;
          self.sessionToken = creds.Token;
          self.expireTime = new Date(creds.Expiration);
        }
        callback(err);
      });
    }
func_code_string: function refresh(callback) {
      var self = this;
      if (!callback) callback = function(err) { if (err) throw err; };
  
      self.metadataService.loadCredentials(function (err, creds) {
        if (!err) {
          self.expired = false;
          self.metadata = creds;
          self.accessKeyId = creds.AccessKeyId;
          self.secretAccessKey = creds.SecretAccessKey;
          self.sessionToken = creds.Token;
          self.expireTime = new Date(creds.Expiration);
        }
        callback(err);
      });
    }
func_documentation_string: Loads the credentials from the instance metadata service
  
  @callback callback function(err)
  Called when the instance metadata service responds (or fails). When
  this callback is called with no error, it means that the credentials
  information has been loaded into the object (as the `accessKeyId`,
  `secretAccessKey`, and `sessionToken` properties).
  @param err [Error] if an error occurred, this value will be filled
  @see get