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/main/java/org/elasticsearch/xpack/security/cli/CertGenUtils.java
import org.elasticsearch.common.network.NetworkAddress;
import org.elasticsearch.common.network.NetworkUtils;
import org.elasticsearch.core.SuppressForbidden;
import java.io.IOException;
import java.math.BigInteger;
import java.net.InetAddress;
import java.security.KeyPair;
import java.security.KeyPairGenerator;
import java.security.KeyStore;
import java.security.NoSuchAlgorithmException;
import java.security.PrivateKey;
import java.security.SecureRandom;
import java.security.cert.Certificate;
import java.security.cert.CertificateException;
import java.security.cert.X509Certificate;
import java.sql.Date;
import java.time.ZoneOffset;
import java.time.ZonedDateTime;
import java.util.HashSet;
import java.util.Locale;
import java.util.Objects;
import java.util.Set;
import javax.net.ssl.X509ExtendedKeyManager;
import javax.net.ssl.X509ExtendedTrustManager;
import javax.security.auth.x500.X500Principal;
/**
 * Utility methods that deal with {@link Certificate}, {@link KeyStore}, {@link X509ExtendedTrustManager}, {@link X509ExtendedKeyManager}
 * and other certificate related objects.
 */
public class CertGenUtils {