In this mode, mitmproxy accepts proxy requests and unconditionally forwards all
requests to a specified upstream proxy server. This is in contrast to <a
href="@!urlTo("reverseproxy.html")!@">reverse proxy mode</a>, in which
mitmproxy forwards ordinary HTTP requests to an upstream server.

<table class="table">
    <tbody>
        <tr>
            <th width="20%">command-line</th> <td>-U http://hostname[:port]</td>
        </tr>
    </tbody>
</table>

Here, **schema** is one of http, https, http2https or https2http. The latter
two extended schema specifications control the use of HTTP and HTTPS on
mitmproxy and the upstream server. You can indicate that mitmproxy should use
HTTP, and the upstream server uses HTTPS like this:

	http2https://hostname:port

And you can indicate that mitmproxy should use HTTPS while the upstream
service uses HTTP like this:

	https2http://hostname:port