'Returns a key for HMAC-SHA1 signature as specified at:
http://oauth.net/core/1.0a/#rfc.section.9.2.
:param str consumer_secret:
:attr:`.core.Consumer.secret`
:param str token_secret:
Access token secret as specified in
http://oauth.net/core/1.0a/#anchor3.
:returns:
Key to sign the request with.'

@classmethod
def _create_key(cls, consumer_secret, token_secret=''):

    return _join_by_ampersand(consumer_secret, (token_secret or ''))
