[Bug] Preemptively refresh tokens in the background

[rymeskar]

Which version of MSAL.NET are you using?
Latest

Platform
All

What authentication flow has the issue?
All with the support of refresh_in coming from eSTS.

Repro

Right now, the request that performs the preemptive cache refresh before expiry of a token gets a live latency hit. As discussed with @bgavrilMS, this is not intended behavior.

Expected behavior

The expectation is that the preemptive refresh happens in the background, with the initial cached token being immediately returned. Thus, the request is not burdened with the latency of communication with eSTS and seting the token to cache.