Selective scrape via query parameters

I'm looking at adopting pg_exporter as a potential replacement for the CloudNative-PG built-in scraper I currently use.

CNPG doesn't support this either, but I was considering implementing it for CNPG and wonder if I should do so for pg_exporter instead.

Do you have any advice on how I might go about adding support for scraping selected subsets of metrics, specified by tag-set, with query parameters?

I want to scrape different subsets at different frequencies without having to deploy multiple instances of the scraper. This can't be done with command-line or env-var level tags.

E.g. I want to scrape /metrics?tags=expensive_metrics,wide_cardinality_metrics every 5min, and /metrics?cheap_narrow_metrics every 30s.

The scraper's caching feature makes this a less pressing need than it is in other scrapers, but since it already has tagging I'm wondering if it might be fairly easy to add. I can't immediately see how to access the query params from/within promhttp in order to apply them selectively though. Do you know if this might be possible, and have any ideas about how? If so, I can see if I can cook up a patch if my initial PoC with this scraper works out.

(See related https://github.com/Vonng/pg_exporter/issues/41, #43 )