Add a way to manually clear cached badge responses

[dohyeon5626]

📋 Description

GitHub-related badges return an error response when a repository is private because the repository is not publicly accessible, which is expected behavior.

However, after making the repository public, the badge can continue showing the previous error message for some time because the error response is still cached.

Although the badge URL becomes valid immediately after the visibility change, it can still appear broken until the cache expires naturally.
GitHub’s Camo cache can be purged manually, but Shields’ own cache still keeps the old error response.

It would be helpful to have a way to manually clear the cached response for a specific badge URL.

[PyvesB]

Hello @dohyeon5626 👋🏻

Thanks for the idea.

We rely on Cloudfare for most of our caching functionality. Clearing a specific badge out of their cache would require integrating with Cloudfare's purge API, which would be non trivial.

Even if we did so, we would open the door to abuses, folks could maliciously clear the cache for our most popular badges, which would increase load on our servers or eat up rate limits for the upstream APIs we call. We'd essentially be opening an attack vector for a form of denial of service. We'd need to enforce strict rate limits on the purge feature, per-URL cooldowns, etc.

In an ideal world, it'd occasionally be handy to be able to manually clear a cache. But realistically speaking, I don't think we'll ever implement it.