certs: Use TWEAK domain certs if set

[Rijul-A]

Web proxy extension of snikket-im/snikket-server#69

[mwild1]

👋

I'm trying to piece things together so we could rebase and merge this PR prior to the upcoming release. I'm not aiming for full support of split-domain setups in this release, but I'd like to make any small safe steps that we can towards it. This seems like one!

I see that SNIKKET_TWEAK_CERT_DOMAIN is being pulled from SNIKKET_TWEAK_XMPP_DOMAIN. But in the case of a split-domain setup, we want nginx to have certs for the web domain, right?

[Rijul-A]

Hey Matt! How have you been?

I have forgotten some of what I wrote back then but you are correct. If SNIKKET_TWEAK_XMPP_DOMAIN is set, the jids are of the form user@SNIKKET_TWEAK_XMPP_DOMAIN and the web portal is still hosted on SNIKKET_DOMAIN. This means that certificates for SNIKKET_DOMAIN should be used.