Allow referrer for external websites for better analytics

[yathomasi]

As per Slack Discussion Thread,

Thanks, @mvshmakov for the deep dive:

Plausible identifies sources in 2 ways:

1. HTTP Referrer header.
2. UTM tags.

dvc.org has nofollow noopener noreferrer on all links and does not use manual UTM tags on any of them (proof attached). So, Plausible, in the case of dvc.org/docs/studio -> studio.iterative.ai/* requests, does not have a way to infer the source, so tags the request with “other”.

Screenshot

We cannot do anything with it on the Studio side because of the browser privacy features and the way Plausible works. Suggested solutions:

1. Allow referrer header in the links on dvc.org (and on all the rest of our websites that we want to track Studio links). I’m in favor of this option.
2. Manually UTM-tag all links that direct users to the Studio.

[yathomasi]

I would also prefer option 1 mentioned as mentioned by @mvshmakov. Also, as of 2023, it's already been years that major browsers have shipped with the fix.

1. It's not a recommendation but we might consider removing (as it will quick and straight forward solution) the noopener noreferrer from the rel attribute as I see almost every roughly almost more than 90% of traffic comes from the latest version of browsers.
2. Here is the source logic behind the external links. Here, we can create a domain whitelist and allow referrers.
3. This doesn't directly affect users or websites SEOs so I would say it's nice to have feature.

cc: @tapadipti @iterative/studio-frontend

[tapadipti]

@yathomasi @mvshmakov A clarification: The issue is not only with redirects to Studio, it's also with redirects to our other sites (eg, iterative.ai). Option 1 will address issues with all these redirects, right?

[mvshmakov]

The issue is not only with redirects to Studio, it's also with redirects to our other sites (eg, iterative.ai). Option 1 will address issues with all these redirects, right?

It depends on the analytics implementation on the respected websites. If analytics is using document.referrer to identify the referrer, then it'd work. Plausible on all websites will work.

Note that the fix in this repo would only work in one side. E.g., we still have the same noopener noreferrer thing on links on the Studio side, so dvc.org -> studio.iterative.ai would be tracked, but studio.iterative.ai -> dvc.org would not. This requires a separate fix on the Studio and other websites side.

@yathomasi I've dropped the support of noopener noreferrer in the Studio: https://github.com/iterative/studio/pull/5746. You can consider adding the list of trusted domains if you want to support older browsers.

[mvshmakov]

Update: we've decided to go with rel="noopener", despite it is being implied on all modern browsers.