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
t.addSuppressed(ex);
            }
            try {
                deleteDirectory(tempGeneratedTlsCertsDir);
            } catch (Exception ex) {
                t.addSuppressed(ex);
            }
            throw t;
        }
        try {
            
            final Environment localFinalEnv = env;
            final DateTimeFormatter dateTimeFormatter = DateTimeFormatter.ofPattern("dd-MM-yyyy HH:mm:ss", Locale.ROOT);
            List<String> existingConfigLines = Files.readAllLines(ymlPath, StandardCharsets.UTF_8);
            fullyWriteFile(env.configFile(), "elasticsearch.yml", true, stream -> {
                try (BufferedWriter bw = new BufferedWriter(new OutputStreamWriter(stream, StandardCharsets.UTF_8))) {
                    
                    for (String line : existingConfigLines) {
                        bw.write(line);
                        bw.newLine();
                    }
                    bw.newLine();
                    bw.write(AUTO_CONFIGURATION_START_MARKER);
                    bw.newLine();
                    bw.write("#");
                    bw.newLine();
                    bw.write("# The following settings, TLS certificates, and keys have been automatically      ");
                    bw.newLine();
                    bw.write("# generated to configure Elasticsearch security features on ");
                    bw.write(autoConfigDate.format(dateTimeFormatter));