Indicate the signature mechanism for the API

[earth2marsh]

As we relax the idea that paths must be unique, it can complicate the signature evaluation process. Consider adding a signature style as part of the info block, such as path+verb, action-header, or similar? (haven't thought this through fully, I just wanted to stub out the idea.)

[captainsafia]

I came across this discussion item while reasoning through what role operation IDs play in the v4 spec. Is the idea that these signatures would replace the existing operation ID property?

[earth2marsh]

We discussed signatures on today's call. Video will be posted here: #107 (comment) (and see also the doc mentioned in the comments)

[earth2marsh]

We're planning to pick up the signature topic again starting next week. The last time we discussed this, we ended up with this document. (It may have some useful concepts, but it was early, so it may also have some dead ends!)