@staticmethod<EOL><INDENT>def _to_safe_path_param_name(matched_parameter):<DEDENT>
return '<STR_LIT:_>' + base64.b32encode(matched_parameter).rstrip('<STR_LIT:=>')<EOL>
Creates a safe string to be used as a regex group name.

        Only alphanumeric characters and underscore are allowed in variable name
        tokens, and numeric are not allowed as the first character.

        We cast the matched_parameter to base32 (since the alphabet is safe),
        strip the padding (= not safe) and prepend with _, since we know a token
        can begin with underscore.

        Args:
          matched_parameter: A string containing the parameter matched from the URL
            template.

        Returns:
          A string that's safe to be used as a regex group name.