Fix: PIA port forwarding (#427)

- Update PIA token URL
- Change base64 decoding to standard decoding
- Add unit tests
- Remove environment variable `GODEBUG=x509ignoreCN=0`
- Fixes #423 
- Fixes #292 
- Closes #264 
- Closes #293

Dockerfile

@@ -147,5 +147,4 @@ RUN apk add -q --progress --no-cache --update openvpn ca-certificates iptables i
     deluser unbound && \
     mkdir /gluetun
 # TODO remove once SAN is added to PIA servers certificates, see https://github.com/pia-foss/manual-connections/issues/10
-ENV GODEBUG=x509ignoreCN=0
 COPY --from=build /tmp/gobuild/entrypoint /entrypoint