feat(docs): Add section on CoAP

[chrysn]

Description

As per today's meeting, I've pulled ahead writing CoAP documentation to give all involved a better overview of how the security protocols interact.

Unlike what we otherwise do with the book, this is ahead of the implementation (covering some of the roadmap but also some things not in there in the current iteration). As this matures, the annotation of "we don't have this yet" will move from page-wide into sections.

Open questions

Should we aim for this to be merged with the disclaimer in, or do we rather keep it as a PR until most of it is implemented? I'm leaning toward the former, especially because the book is also a good reference for developers.

Change checklist

• I have cleaned up my commit history and squashed fixup commits.
• I have followed the Coding Conventions.
• I have performed a self-review of my own code.
• I have made corresponding changes to the documentation.

[elenaf9]

Great chapter!

[chrysn]

Thanks, good points, all addressed. I've left the non-trivial ones unresolved (except the one I opened myself).

While most fixups are precise (thanks to git absorb), I think this can be squashed into a single commit when accepted.

[kaspar030]

I really want the OSCORE/EDHOC/ACE stack optional.

if we manage to fully tame the added complexity, this can be changed down the line, but initially just to make that complexity visible, it has to be optional.

[kaspar030]

I much prefer this restructured version!

[chrysn]

I've done an editing pass fixing some remaining typos, grammer errors or inconsistencies (finally found a better subsection title, s/ACE during development/Using ACE from the host during development/ is now consistent with the earlier heading "Interacting with a RIOT-rs CoAP server from the host"), and applied fixes that got lost over non-git contributions.

@kaspar030, if you're fine with this and can press the button, I'll squash.

[kaspar030]

@kaspar030, if you're fine with this and can press the button, I'll squash.

let's go!

[kaspar030]

Feel free to "gq" the paragraphs to a consistent look ...

[chrysn]

I'm not sure we have an official style guide – I've squashed things rather broadly because the different kinds of edits didn't commute well, now it's "create, restructure, editorial fixes". This captures the genesis without being spread too thin into "fix(doc/coap): Typos".

Hope that's fine.

[chrysn]

Feel free to "gq" the paragraphs to a consistent look ...

I expect to review later edits on those, so I'd prefer not to; https://sembr.org/ says it better than I can.