def parse_authorization_header(value):
    """Parse an HTTP basic/digest authorization header transmitted by the web
    browser.  The return value is either `None` if the header was invalid or
    not given, otherwise an :class:`~werkzeug.datastructures.Authorization`
    object.

    :param value: the authorization header to parse.
    :return: a :class:`~werkzeug.datastructures.Authorization` object or `None`.
    """
    if not value:
        return
    value = wsgi_to_bytes(value)
    try:
        auth_type, auth_info = value.split(None, 1)
        auth_type = auth_type.lower()
    except ValueError:
        return
    if auth_type == b'basic':
        try:
            username, password = base64.b64decode(auth_info).split(b':', 1)
        except Exception as e:
            return
        return Authorization('basic', {'username':  bytes_to_wsgi(username),
                                       'password': bytes_to_wsgi(password)})
    elif auth_type == b'digest':
        auth_map = parse_dict_header(auth_info)
        for key in 'username', 'realm', 'nonce', 'uri', 'response':
            if not key in auth_map:
                return
        if 'qop' in auth_map:
            if not auth_map.get('nc') or not auth_map.get('cnonce'):
                return
        return Authorization('digest', auth_map)
Parse an HTTP basic/digest authorization header transmitted by the web
    browser.  The return value is either `None` if the header was invalid or
    not given, otherwise an :class:`~werkzeug.datastructures.Authorization`
    object.

    :param value: the authorization header to parse.
    :return: a :class:`~werkzeug.datastructures.Authorization` object or `None`.