Add support for client certificates (mTLS)

[amne]

By the looks of it the branch "client-certificate-3" should allow a user to configure mTLS and use it with the iOS app just like it is today possible on Android.

[bgoncal]

This branch is a complete POC, it's not mergeable.

[amne]

Of course some work is needed to update it. It is more than 500 commits behind.

[bgoncal]

Not "some work", proper work. I have worked on that branch to validate mTLS behavior on iPhone while in foreground, background, coming from watch and CarPlay, it's far from production code. On top of that the results were not all good, background certificates challenges were not always forwarded by iOS to the App so they were failing.

[amne]

I didn't mean it in a diminishing way. Any work is work and it takes time. I'm not an iOS dev but I also won't play ignorant and say "how hard can it be". I trust you that it is indeed hard. But I also trust the there are experienced members in this community that can make it happen. My only intention here was to have a signal to measure how many people want this capability in the iOS app. I'm sure a lot would like to have this even if limited to the iOS app only.

[bgoncal]

No worries, I did not take it personal, I was just trying to make it clear that there is nothing ready and not even close-to-ready to be merged.
It's clear by other discussions in github and Home Assistant community that this is a feature that the community really wants, but to implement it properly it takes a lot of effort and on top of that these complications that iOS brings when using client certificates in background.

Rest assured this wasn't forgotten in Open Home Foundation either, the topic comes up frequently.

[brstgt]

I appreciate all the work that goes into HA and I understand that every contribution must be solid but this feature would be very valuable for probably very many people looking at the discussions in the past and I also ran into exactly this issue when trying to secure the IOS app