In a micro-service environment, a request to one service will often result in sub-requests being made to other services. In these sub-requests you may want to pass along some contextual metadata so that the next service does not have to look it up again.
Metacontext allows you to pass along a JSON map of metadata without changing the API contract. It is a small wrapper that simplifies the manipulation of JSON bodies to include a metadata section that can be parsed out by the receiving service.
See the example for usage.
The idea behind this is that it would be used here and there in places where something quick and dirty is all that's needed. A more full fledged solution should be considered if you are finding that this functionality is needed in a lot of places.