[Feature]: handle ?ref & ?utm_source as fallback values for referer header

[JonasDoesThings]

Feature Summary

Hey, I think it would be good to use the query parameters "?ref=" and "?utm_source" (and potentially also ?source) as values for the referer if the header is not present.

To implement this, we would need to extend the logic in the tracker's getBrowserReferrer function.

Component

@counterscale/tracker

Additional Context

Plausible checks these parameters, if any of them is present, they are used instead of the referrer header:

tagged_source =
      request.query_params["utm_source"] ||
        request.query_params["source"] ||
        request.query_params["ref"]

source.ex#L54

Pirsch Analytics checks the Referrer header first, and uses these parameters if the Referrer header is null or empty:

export const PIRSCH_REFERRER_QUERY_PARAMETERS = ["ref", "referer", "referrer", "source", "utm_source"] as const;

constants.ts#L5

[stordahl]

@JonasDoesThings Thanks for opening this issue - seems like a good idea to me. I have a few things in-flight currently so want to wrap those up before I dive into this, but feel free to submit a PR if you'd like! Seems pretty straight forward to me

[stordahl]

closed by #240