Please consider to support tailor header value for key-rate-limit and cluster-key-rate-limit.

[jaggerwang]

Why do you need it?

Sometimes we need to use part value of some header to limit request rate, for example, there is a header Authorization: ApiKey <hash> and we only want to use the hash part as the limit key.

How could it be?

Allow prefix or suffix trim of header value, or using regex to capture the limit key.