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
bw.newLine();
                    bw.write("#");
                    
                    bw.newLine();
                    bw.write("# --------------------------------------------------------------------------------");
                    bw.newLine();
                    bw.newLine();
                    bw.write("# Enable security features");
                    bw.newLine();
                    bw.write(XPackSettings.SECURITY_ENABLED.getKey() + ": true");
                    bw.newLine();
                    bw.newLine();
                    
                    if (false == (localFinalEnv.settings().hasValue(XPackSettings.ENROLLMENT_ENABLED.getKey())
                        && false == XPackSettings.ENROLLMENT_ENABLED.get(localFinalEnv.settings()))) {
                        bw.write(XPackSettings.ENROLLMENT_ENABLED.getKey() + ": true");
                        bw.newLine();
                        bw.newLine();
                    }
                    bw.write("# Enable encryption for HTTP API client connections, such as Kibana, Logstash, and Agents");
                    bw.newLine();
                    bw.write("xpack.security.http.ssl:");
                    bw.newLine();
                    bw.write("  enabled: true");
                    bw.newLine();
                    bw.write("  keystore.path: " + TLS_GENERATED_CERTS_DIR_NAME + "/" + HTTP_AUTOGENERATED_KEYSTORE_NAME + ".p12");
                    bw.newLine();
                    bw.newLine();
                    bw.write("# Enable encryption and mutual authentication between cluster nodes");
                    bw.newLine();