'Verifies that the challenge is a Bearer challenge and returns the key=value pairs.'

def _validate_challenge(self, challenge):

    bearer_string = 'Bearer    '
    if (not challenge):
        raise ValueError('Challenge    cannot    be    empty')
    challenge = challenge.strip()
    if (not challenge.startswith(bearer_string)):
        raise ValueError('Challenge    is    not    Bearer')
    return challenge[len(bearer_string):]
