CORS settings on testnet GRPC endpoint are broken again

[hdevalence]

Describe the bug

https://buf.build/studio/penumbra-zone/penumbra/penumbra.core.app.v1.QueryService/AppParameters?target=https%3A%2F%2Fgrpc.testnet.penumbra.zone&selectedProtocol=grpc-web&share=s2KqrgUA

Does not work in FF with a CORS error.

[conorsch]

Tested this shortly after you reported it, and was able to reproduce, although I didn't bother to screenshot it. Intriguingly, the problem was also evident on the solo node https://solo-pd.testnet.plinfra.net (buf studio link), so it definitely wasn't any reverse-proxies that we run causing the problem. We added an integration test in #3870 to guard against regressions, and that hasn't failed, and polling the endpoints directly shows that they're still serving correctly:

curl results on endpoint calls

❯ curl -I https://grpc.testnet.penumbra.zone
HTTP/2 200
access-control-allow-origin: *
access-control-expose-headers: *
content-type: text/html
date: Mon, 06 May 2024 15:05:08 GMT
vary: origin
vary: access-control-request-method
vary: access-control-request-headers
content-length: 481

❯ curl -I https://solo-pd.testnet.plinfra.net
HTTP/2 200
content-type: text/html
content-length: 481
access-control-allow-origin: *
vary: origin
vary: access-control-request-method
vary: access-control-request-headers
access-control-expose-headers: *
date: Mon, 06 May 2024 15:05:19 GMT

Testing this morning, however, showed it's working just fine:

No changes were made to any of our deployments. Therefore I believe this a transitory change on Buf's end, although I can't find a citation for that. I also made sure to test in Chrome, and Buf Studio is working well with both our endpoints linked above. I'm closing this issue for now, but please re-open if you are still having problems!