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/AutoConfigureNodeTests.java
Files.write(tempDir.resolve("config").resolve("elasticsearch.yml"), List.of(), CREATE_NEW);
            X509Certificate httpCertificate = runAutoConfigAndReturnHTTPCertificate(
                tempDir,
                Settings.builder()
                    .put(NetworkService.GLOBAL_NETWORK_PUBLISH_HOST_SETTING.getKey(), "172.168.1.100")
                    .put(HttpTransportSettings.SETTING_HTTP_HOST.getKey(), "10.10.10.100")
                    .build()
            );
            assertThat(checkGeneralNameSan(httpCertificate, "dummy.test.hostname", GeneralName.dNSName), is(true));
            assertThat(checkGeneralNameSan(httpCertificate, "localhost", GeneralName.dNSName), is(true));
            assertThat(checkGeneralNameSan(httpCertificate, "172.168.1.100", GeneralName.iPAddress), is(true));
            assertThat(checkGeneralNameSan(httpCertificate, "10.10.10.100", GeneralName.iPAddress), is(false));
        } finally {
            deleteDirectory(tempDir);
        }
        
        tempDir = createTempDir();
        try {
            Files.createDirectory(tempDir.resolve("config"));
            
            Files.write(tempDir.resolve("config").resolve("elasticsearch.yml"), List.of(), CREATE_NEW);
            X509Certificate httpCertificate = runAutoConfigAndReturnHTTPCertificate(
                tempDir,
                Settings.builder()
                    .put(NetworkService.GLOBAL_NETWORK_HOST_SETTING.getKey(), "172.168.1.100")
                    .put(HttpTransportSettings.SETTING_HTTP_PUBLISH_HOST.getKey(), "10.10.10.100")
                    .build()
            );
            assertThat(checkGeneralNameSan(httpCertificate, "dummy.test.hostname", GeneralName.dNSName), is(true));