mitmproxy/doc-src/proxyauth.html

Asks the user for authentication before they are permitted to use the proxy.
Authentication headers are stripped from the flows, so they are not passed to
upstream servers. For now, only HTTP Basic authentication is supported.

<table class="table">
    <tbody>
        <tr>
            <th width="20%">command-line</th>
            <td>
                <ul>
                    <li>--nonanonymous</li>

                    <li>--singleuser USER</li>

                    <li>--htpasswd PATH</li>
                </ul>
            </td>
        </tr>
    </tbody>
</table>