Access-controlled search for Rocket.Chat

[mrsimpson]

Motivation

As a user of Assistify (with the Rocket.Chat frontend), I want to be able to find conversations I had in the past. Thus, I would like to search also normal channels and even private conversations with a full-text search.

Implementation boundaries

• This involves modifications to Rocket.Chat core. All this modification shall be contributed. See [NEW] Connection of external search providers in spotlight RocketChat/feature-requests#745 for the necessary boundaries. Commit to in order to keep communication simple
• The data replicated shall include an access control list. The API will propagate the user searching. => The user shall only find messages of rooms which he'll be able to open afterwards.
• The events relevant to the external search are denoted in the linked issue. Particular reacting on changes to the permissions might invalidate a lot of the ACLs.
• It might make sense to add methods to the API which allow the search provider to propagate a status. But that's surely something you already have got experiences with ;)