Performance

I had an in-memory cache on permissions (invalidates at each user update or after 5s)

for performance testing results : see applications/hubl#675 (comment 37112)

It's the second quick-win step.

We should evolve this 'naive' implementation with a configurable cache connected to a redis or memcache db.

There's still some inacceptable timing (on users container : 300+ ms, should be less than 50ms)