How to provide access to the intranet via vpn from the outside with only raspberry?

Question

VPN

Given: 1.
Raspberry Pi 3b+ (rasp) (Raspbian)
2. Server with white ip (serv) (Ubuntu 16.04 ) There is access to the Internet with Rasp (at 80 and 443) Task: 1. Access to the intranet, where there is a place for several people. Traffic proxying in the following way somePC->serv->rasp->intranet. Ssh between sort and the server on certificates. Automatically, when rasp is connected to a network where there is Internet, port 22 is forwarded from rasp to serv on port 6622.
There were attempts to raise OpenVPN to rasp (pivpn by default) and tunnel through ssh (ssh -fN -R \*:1195:rasp_ip:1194 [email protected]_ip) port 1194 from rasp to 1195 serv, but this scheme did not work. There was also an attempt to send 1194 through ngrok, it also did not work out.
Comrades, tell me the working scheme, the easiest way to implement such a physical backdoor (for needs within the law :)
Or at least tell me a suitable manual or article.

Answer 1

why tunnel? pivpn not connecting directly to the server? what if you hang up ovpn on port 80 at the server and connect with rasp? I understand that your ports are cut on the rasp side, or is certain traffic blocked?