Add a caveat extractor system?

[waxzce]

In many projects, there are needs of data extraction from the caveat, and at the moment, extraction has to be made manually iteration on top of macaroon after the validation. This issue is made to discuss if we need to add a value extractor to caveat management in jmacaroons.

I quickly did something on a project, it a crypto token translation system, from macaroons to warp10 tokens, it's far from perfect, but it can be a good starting point https://github.com/CleverCloud/warp10-macaroons-plugin

Do you think I have to explore the possibility and make a pull request?

[jaxley]

I was thinking that this is something that will be very helpful. The reference implementation alludes to various APIs for recovering first and third party caveats. Right now, third party caveats get split into three different caveat packets that you'd have to linearly process caveats or backtrack just to get the caveat ID for a given third party caveat.