IdP instrumentation / metrics

[Tom Zeller]

> At this point we're just brainstorming, so anything is welcome.
> 
> Most of this is probably post-3.3 work, but the requirements will help make some decisions about libraries we might incorporate in 3.3 to get some experience.

Perhaps we could include metrics-spring[1] in IdP 3.3, leaving the XML config file in conf/ rather than system/conf, as that evolves. But I haven’t reviewed anything, just looked at the readme.

[1] https://github.com/ryantenney/metrics-spring