Return a caveat that specifies that the time that it is checked at
    should be before t.
    :param t is a a UTC date in - use datetime.utcnow, not datetime.now

def time_before_caveat(t):
    '''Return a caveat that specifies that the time that it is checked at
    should be before t.
    :param t is a a UTC date in - use datetime.utcnow, not datetime.now
    '''

    return _first_party(COND_TIME_BEFORE,
                        pyrfc3339.generate(t, accept_naive=True,
                                           microseconds=True))