'Add an auth level URI alias to this request.
@param auth_level_uri: The auth level URI to send in the
request.
@param alias: The namespace alias to use for this auth level
in this message. May be None if the alias is not
important.'

def _addAuthLevelAlias(self, auth_level_uri, alias=None):

    if (alias is None):
        try:
            alias = self._getAlias(auth_level_uri)
        except KeyError:
            alias = self._generateAlias()
    else:
        existing_uri = self.auth_level_aliases.get(alias)
        if ((existing_uri is not None) and (existing_uri != auth_level_uri)):
            raise KeyError('Attempting    to    redefine    alias    %r    from    %r    to    %r', alias, existing_uri, auth_level_uri)
    self.auth_level_aliases[alias] = auth_level_uri
