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
"xpack.security.http.ssl.keystore.secure_password",
                    "autoconfiguration.password_hash"
                );
                for (String setting : secureSettingsToRemove) {
                    if (existingKeystore.getSettingNames().contains(setting) == false) {
                        throw new UserException(
                            ExitCodes.IO_ERROR,
                            "Aborting enrolling to cluster. Unable to remove existing security configuration, "
                                + "elasticsearch.keystore did not contain expected setting ["
                                + setting
                                + "]."
                        );
                    }
                    existingKeystore.remove(setting);
                }
                existingKeystore.save(env.configFile(), keystorePassword.getChars());
            } catch (Exception e) {
                terminal.errorPrintln(Terminal.Verbosity.VERBOSE, "");
                terminal.errorPrintln(Terminal.Verbosity.VERBOSE, ExceptionsHelper.stackTrace(e));
                terminal.errorPrintln(Terminal.Verbosity.VERBOSE, "");
                throw new UserException(
                    ExitCodes.IO_ERROR,
                    "Aborting enrolling to cluster. Unable to remove existing secure settings. Error was: " + e.getMessage(),
                    e
                );
            }
        }
    }
}