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
if (period.getYears() != 0) {
            parts.add(period.getYears() + "y");
        }
        if (period.getMonths() != 0) {
            parts.add(period.getMonths() + "m");
        }
        if (period.getDays() != 0) {
            parts.add(period.getDays() + "d");
        }
        return Strings.collectionToCommaDelimitedString(parts);
    }
    private Path requestPath(String prompt, Terminal terminal, Environment env, boolean requireExisting) {
        for (;;) {
            final String input = terminal.readText(prompt);
            final Path path = env.configFile().resolve(input).toAbsolutePath();
            if (path.getFileName() == null) {
                terminal.println(Terminal.Verbosity.SILENT, input + " is not a valid file");
                continue;
            }
            if (requireExisting == false || Files.isReadable(path)) {
                return path;
            }
            if (Files.notExists(path)) {
                terminal.println(Terminal.Verbosity.SILENT, "The file " + path + " does not exist");
            } else {
                terminal.println(Terminal.Verbosity.SILENT, "The file " + path + " cannot be read");
            }
        }
    }
    static FileType guessFileType(Path path, Terminal terminal) {