IPEX apply, offer, agree implementation

[iFergal]

I would like to get these added to KERIA and Signify-TS as it's something my team needs. Happy to give it a try myself, perhaps apply -> offer -> agree for a normal AID to begin with (multisig, spurn later).

Understanding the existing impl:
I've taken a look at the existing grant and apply messages in KERIA. The messages are parsed, pushed onto the exchanging deck to be sent to recipients and then pushed to either the grants or admits deck in agent.ts. From what I understand: Granter will send the other necessary material such as registry events, and Admitter will parse the ACDC, issuance and anchoring events attached to the admit message.

Q: Admitter will actually first check to see if there's a grant listed (otherwise invalid) - in case the grant is missing, or there is an issue parsing the attachments (e.g. the ACDC itself) hasn't the admit message already been sent to other parties using exchanging in ipexing.py? Curious if we should should check the grant is listed before sending the message onwards.

New messages:
apply and agree messages seem straight forward - do I need to do anything more other than sending the message to recipients in KERIA?

For offer I need a metadata ACDC, not sure if there's anything already available for this. Looking at the IPEX tests in keripy, it seems to just use a normal ACDC. Though it shouldn't be too hard to strip it down to a metadata ACDC and re-calculate the SAID.

[iFergal]

@pfeairheller Have some questions re Admitter flow and the metadata ACDC in the description above if you have time to answer. Thanks :)

Just going to start looking at this today/this week - have been stuck on other things.

[lenkan]

@iFergal can this be closed now?