Security context confiugration format

[chrysn]

The current credentials.diag format (and the parts that ) is a bit of a mess, owing in no small part to its history of organically growing from what was originally just DTLS support and very vague idea of what ACE-OSCORE responses might look like.

Things that should be improved:

• Multi-file support. A credential may be referred to in different contexts.
  • In particular, aiocoap-keygen and any future --tofu switch (maybe even default mode?) should have an option to write somewhere.
• Default system-wide files. aiocoap tools will use those unless something --no-default-credentials is passed, libraries should get an easy way to opt in to it.
• Clean up {14:{8:…}}. Lakers justifiedly switched to having programming language names for the different credentials types, given that putting them into CRED_x requires understanding what they are anyway, so they can get names in the config language too. This will make things consistent with Ariel OS.
• The current form of ingesting items through a type builder is a bit awkward, and should at least get thorough refactoring. In particular, psk_hex and psk_bin was probably a mistake. Right now, I'd go more towards having TOML files supported easily, and there the JSON-model structure would be

  {"psk": {"ascii": "correct horse battery staple"}}
  

  and then the ingesting entity asks to make a binary string out of it, whereupon any map gets pulled through some to-binary conversion that might tolerate a single "ascii", "hex" or "edn" key. (Not sure yet what to do with places that are typically encoded-CBOR shaped, can we put the item in there directly if the format happens to be EDN? Maybe <<{}>> which is kinda nice when it comes to non-deterministically encoded stuff where that is allowed).

Further notes:

• IETF122 hackathon notes "EDHOC’s ~/.ssh/"

Related issues:

• https://github.com/chrysn/aiocoap/issues/383
• https://github.com/chrysn/aiocoap/issues/377
• The whole topic of having fixed configurations for peers and proxies
• Setting something easy from the CLI (eg. kicking off opportunistic EDHOC or TOFU)

[chrysn]

TOML would now be an easier candidate since https://github.com/chrysn/aiocoap/issues/391