token server scale-out solution

## Issue Description
all requests need to go through token server when use cluster flow control, so I have the following questions
1. whether there is stand-alone performance data of the token server
2. Is there a scale-out solution for token server

Review the cluster flow-control path and token server architecture first, then look for existing standalone performance data. The issue is complete when the performance characteristics and a concrete, validated scale-out solution are documented.

Written by the indexing model from the issue text.