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/AutoConfigureNode.java
if (nodeKeystore.getSettingNames().contains("xpack.security.transport.ssl.keystore.secure_password")
                || nodeKeystore.getSettingNames().contains("xpack.security.transport.ssl.truststore.secure_password")
                || nodeKeystore.getSettingNames().contains("xpack.security.http.ssl.keystore.secure_password")) {
                
                
                
                
                throw new UserException(
                    ExitCodes.CONFIG,
                    "Aborting auto configuration because the node keystore contains password settings already"
                );
            }
            try (SecureString transportKeystorePassword = newKeystorePassword()) {
                KeyStore transportKeystore = KeyStore.getInstance("PKCS12");
                transportKeystore.load(null);
                
                transportKeystore.setKeyEntry(
                    TRANSPORT_KEY_KEYSTORE_ENTRY,
                    transportKey,
                    transportKeystorePassword.getChars(),
                    new Certificate[] { transportCert }
                );
                transportKeystore.setCertificateEntry(TRANSPORT_CA_CERT_KEYSTORE_ENTRY, transportCaCert);
                fullyWriteFile(
                    tempGeneratedTlsCertsDir,
                    TRANSPORT_AUTOGENERATED_KEYSTORE_NAME + ".p12",
                    false,
                    inReconfigureMode ? ELASTICSEARCH_GROUP_OWNER : null,
                    stream -> transportKeystore.store(stream, transportKeystorePassword.getChars())
                );