We generate certificates that are intended to be used for server authentication in a couple of places:

- `bin/elasticsearch-certutil http` command  ( See `CertGenUtils.generateSignedCertificate` in `HttpCertificateCommand` )
- TLS auto-configuraion for node startup ( see [`AutoConfigureNode`](https://github.com/elastic/elasticsearch/blob/814f7f9f52cb8c05db6465b9bfc818ea5d76c575/x-pack/plugin/security/cli/src/main/java/org/elasticsearch/xpack/security/cli/AutoConfigureNode.java#L454) )

In these cases we know that the certificate is meant to be used for server authentication, so we can set Extended Key Usage extension to `1.3.6.1.5.5.7.3.1`
x-pack/plugin/security/cli/src/test/java/org/elasticsearch/xpack/security/cli/HttpCertificateCommandTests.java
for (GeneralName name : names.getNames()) {
            assertThat(name.getTagNo(), oneOf(GeneralName.dNSName, GeneralName.iPAddress));
            if (name.getTagNo() == GeneralName.dNSName) {
                final String dns = DERIA5String.getInstance(name.getName()).getString();
                assertThat(dns, in(hostNames));
            } else if (name.getTagNo() == GeneralName.iPAddress) {
                final String ip = formatIpAddress(DEROctetString.getInstance(name.getName()).getOctets());
                assertThat(ip, in(ipAddresses));
            }
        }
    }
    private void verifyCertificate(
        X509Certificate cert,
        String certificateName,
        int years,
        List<String> hostNames,
        List<String> ipAddresses
    ) throws CertificateParsingException {
        assertThat(cert.getSubjectX500Principal().toString(), is("CN=" + certificateName.replaceAll("\\.", ", DC=")));
        final Collection<List<?>> san = cert.getSubjectAlternativeNames();
        final int expectedSanEntries = hostNames.size() + ipAddresses.size();
        if (expectedSanEntries > 0) {
            assertThat(san, hasSize(expectedSanEntries));
            for (List<?> name : san) {
                assertThat(name, hasSize(2));
                assertThat(name.get(0), Matchers.instanceOf(Integer.class));
                assertThat(name.get(1), Matchers.instanceOf(String.class));
                final Integer tag = (Integer) name.get(0);
                final String value = (String) name.get(1);
                assertThat(tag, oneOf(GeneralName.dNSName, GeneralName.iPAddress));