tsh proxy ssh does not respect HTTP_PROXY

[russjones]

Customer has reported that tbot does not respect HTTP_PROXY when making connections.

[strideynet]

Potentially useful: #10209

---

Things to review

• Any usages of webclient
• Any usages of API client
• Registration
  • Through Proxy
  • Through Auth
• tbot proxy

[strideynet]

Customer reported issue running v9.3.18.

Customer specifically complained about issue when using the generated ssh_config - and hence - tbot proxy ssh.

[strideynet]

dialSSHProxy of tool/tsh/proxy.go does not respect HTTP_PROXY or HTTPS_PROXY:

func dialSSHProxy(ctx context.Context, tc *libclient.TeleportClient, sp sshProxyParams) (net.Conn, error) {
	remoteProxyAddr := net.JoinHostPort(sp.proxyHost, sp.proxyPort)

	if !sp.tlsRouting {
		conn, err := (&net.Dialer{}).DialContext(ctx, "tcp", remoteProxyAddr)
		if err != nil {
			return nil, trace.Wrap(err)
		}
		return conn, nil
	}

	pool, err := tc.LocalAgent().ClientCertPool(sp.clusterName)
	if err != nil {
		return nil, trace.Wrap(err)
	}

	tlsConfig := &tls.Config{
		RootCAs:            pool,
		NextProtos:         []string{string(alpncommon.ProtocolProxySSH)},
		InsecureSkipVerify: tc.InsecureSkipVerify,
		ServerName:         sp.proxyHost,
	}

	conn, err := (&tls.Dialer{Config: tlsConfig}).DialContext(ctx, "tcp", remoteProxyAddr)
	if err != nil {
		return nil, trace.Wrap(err)
	}
	return conn, nil
}

Both dialers here need to use a HTTP Proxy dialer if one has been configured in the environment.

As Machine ID tbot proxy ssh just invokes tsh proxy ssh this is also affected.