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/HttpCertificateCommand.java
default -> {
                terminal.println(Terminal.Verbosity.SILENT, "The file at " + caPath + " isn't a file type that this tool recognises.");
                terminal.println("Please try again with a CA in PKCS#12, JKS or PEM format");
                throw new UserException(ExitCodes.DATA_ERROR, caPath + ": Unrecognized file type");
            }
        }
    }
    private CertificateTool.CAInfo createNewCA(Terminal terminal) {
        terminal.println("A new Certificate Authority will be generated for you");
        printHeader("CA Generation Options", terminal);
        terminal.println("The generated certificate authority will have the following configuration values.");
        terminal.println("These values have been selected based on secure defaults.");
        terminal.println("You should not need to change these values unless you have specific requirements.");
        terminal.println("");
        X500Principal dn = DEFAULT_CA_NAME;
        Period validity = DEFAULT_CA_VALIDITY;
        int keySize = DEFAULT_CA_KEY_SIZE;
        while (true) {
            terminal.println(Terminal.Verbosity.SILENT, "Subject DN: " + dn);
            terminal.println(Terminal.Verbosity.SILENT, "Validity: " + toString(validity));
            terminal.println(Terminal.Verbosity.SILENT, "Key Size: " + keySize);
            terminal.println(Terminal.Verbosity.SILENT, "");
            if (terminal.promptYesNo("Do you wish to change any of these options?", false) == false) {
                break;
            }
            printHeader("What should your CA be named?", terminal);
            terminal.println("Every client that connects to your Elasticsearch cluster will need to trust");
            terminal.println("this custom Certificate Authority.");
            terminal.println("It is helpful to have a meaningful name for this CA");
            terminal.println("");