code: protected function getToken(string $user, string $scope = ''): Slice
      {
          if (!isset($this->tokens[$user]))
          {
              $this->tokens[$user] = $this->authorize($user, [
                  'scope' => $scope
              ]);
          }
  
          return $this->tokens[$user];
      }
docs: @param string $user
  @param string $scope
  
  @return Slice
  
  @throws Invalid