def get_unverified_key():
    """
        Wait for key-exchange to occur, then return the raw unverified SPAKE2
        key.  When this fires, we have not seen any evidence that anyone else
        shares this key (nor have we seen evidence of a failed attack: e.g. a
        payload encrypted with a different key).

        This is only useful for testing, and for noticing a significant delay
        between the key-agreement message and the subsequent key-verification
        ("versions") message.

        :return: the raw unverified SPAKE2 key
        :rtype: ``Deferred[bytes]``
        """
