    def __init__(self, hs):
        super().__init__(hs)

        self.http_client = SimpleHttpClient(hs)
        # We create a blacklisting instance of SimpleHttpClient for contacting identity
        # servers specified by clients
        self.blacklisting_http_client = SimpleHttpClient(
            hs, ip_blacklist=hs.config.federation_ip_range_blacklist
        )
        self.federation_http_client = hs.get_http_client()
        self.hs = hs
A web application accepts a user-controlled input that specifies a link to an external site, and uses that link in a Redirect. This simplifies phishing attacks.