def _format_src_url(self, path, caller_system):
        """
        Ensure path is absolute and use the correct URL format for use with
        cross Azure storage account copy function.

        Args:
            path (str): Path or URL.
            caller_system (pycosio.storage.azure._AzureBaseSystem subclass):
                System calling this method (Can be another Azure system).

        Returns:
            str: URL.
        """
        path = '%s/%s' % (self._endpoint, self.relpath(path))

        # If SAS token available, use it to give cross account copy access.
        if caller_system is not self:
            try:
                path = '%s?%s' % (path, self._storage_parameters['sas_token'])
            except KeyError:
                pass

        return path