Here:

x509.ParseCertificate expects DER-encoded ASN.1 data: https://pkg.go.dev/crypto/x509#ParseCertificate

| ParseCertificate parses a single certificate from the given ASN.1 DER data.

Certificates in ConfigMaps are typically stored in PEM format
Need to use pem.Decode to convert from PEM to DER before parsing.

Tests: https://github.com/golang/go/blob/9ce47e66e8eb7348005f1e45a77a729e7f146a1e/src/crypto/x509/x509_test.go#L601