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
private final boolean inReconfigureMode;
    private final BiFunction<Environment, String, CommandLineHttpClient> clientFunction;
    public AutoConfigureNode(boolean reconfigure, BiFunction<Environment, String, CommandLineHttpClient> clientFunction) {
        super("Generates all the necessary security configuration for a node in a secured cluster");
        
        
        parser.allowsUnrecognizedOptions();
        this.inReconfigureMode = reconfigure;
        this.clientFunction = clientFunction;
    }
    public AutoConfigureNode(boolean reconfigure) {
        this(reconfigure, CommandLineHttpClient::new);
    }
    @Override
    public void execute(Terminal terminal, OptionSet options, Environment env, ProcessInfo processInfo) throws Exception {
        final boolean inEnrollmentMode = options.has(enrollmentTokenParam);
        
        for (Path dataPath : env.dataFiles()) {
            if (Files.isDirectory(dataPath) && false == isDirEmpty(dataPath)) {
                final String msg = "Skipping security auto configuration because it appears that the node is not starting up for the "
                    + "first time. The node might already be part of a cluster and this auto setup utility is designed to configure "
                    + "Security for new clusters only.";
                notifyOfFailure(inEnrollmentMode, terminal, Terminal.Verbosity.VERBOSE, ExitCodes.NOOP, msg);
            }
        }
        
        final Path ymlPath = env.configFile().resolve("elasticsearch.yml");
        
        
        if (false == Files.exists(ymlPath) || false == Files.isRegularFile(ymlPath, LinkOption.NOFOLLOW_LINKS)) {