Comment 3 for bug 1801762

Julian - I hadn't realised there are two gpgv's!

Having found apt's own /usr/lib/methods/gpgv

I have been able to create a shell wrapper that can feed it the expected request headers and parse the response headers to ensure a GPGVOutput: GOODSIG ...

It's a proof of concept right now; if this approach is preferred then I'll tidy it up and publish.