def httpdate(dt):
    """Return a string representation of a date according to RFC 1123 (HTTP/1.1).

    The supplied date must be in UTC.

    :param dt: Datetime object in UTC.
    :type dt: datetime
    :rtype: str
    """
    weekday = ['Mon', 'Tue', 'Wed', 'Thu', 'Fri', 'Sat', 'Sun'][dt.weekday()]
    month = ['Jan', 'Feb', 'Mar', 'Apr', 'May', 'Jun', 'Jul', 'Aug', 'Sep',
        'Oct', 'Nov', 'Dec'][dt.month - 1]
    return (
        '{weekday}, {dt.day:02d} {month} {dt.year:04d} {dt.hour:02d}:{dt.minute:02d}:{dt.second:02d} GMT'
        .format(weekday=weekday, month=month, dt=dt))
