util/oid.go
func GetExtFromCert(cert *x509.Certificate, oid asn1.ObjectIdentifier) *pkix.Extension {
	for i := range cert.Extensions {
		if oid.Equal(cert.Extensions[i].Id) {
			return &(cert.Extensions[i])
		}
	}
	return nil
}
func GetExtFromCert(cert *x509.Certificate, oid asn1.ObjectIdentifier) *pkix.Extension {
	for i := range cert.Extensions {
		if oid.Equal(cert.Extensions[i].Id) {
			return &(cert.Extensions[i])
		}
	}
	return nil
}
// GetExtFromCert returns the extension with the matching OID, if present. If
// the extension if not present, it returns nil.