Rate Limiting of Custom Metrics

The request is to be able to define rate limits for a Custom Metric (custom metrics policy).

Currently if a Custom Metric is defined, and incremented with the policy, it won't be possible to effectively set a rate limit for that metric unless the metric is bound to a mapping rule.

Binding the metric to a mapping rule would result in the metric value to increase:

• according to the custom metric logic
• one more time whenever the mapping rule is hit
  so this is not an option.

The request is to be able to define rate limits that work on a custom metric, that is only increased according to the logic of the custom metrics policy.
This would allow, for example, as for this customer's use case, to only count requests depending on the status code that is returned by their upstream API.