X509 certificate validation more strict in golang 1.25.2

[Reinhard Tartler <siretart@gmail.com>]

Dear fellow Debian Golang Packagers,

I am writing to give you a heads-up about a subtle change in Golang 1.25.2 that makes X.509 certificate verification more strict in the `crypto/x509` package, which is part of the standard library. The change in question is https://github.com/golang/go/commit/3fc4c79fdbb17b9b29ea9f8c29dd780df075d4c4 and I expect it to break rebuilds of several golang packages in Debian.

Specifically, the DNS in the X.509v3 Subject Alternative Name can no longer be empty (cf. https://github.com/etcd-io/etcd/pull/20775#issuecomment-3385325872). This change caused #1117747. I have also seen a similar issue when rebuilding `sigstore-go`, and I plan to file a proper bug report later.

I hope this heads-up saves valuable time for others who are surprised by test failures containing the error: "x509: SAN rfc822Name is malformed".

Best regards,

Reinhard

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regards,
    Reinhard