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
static final int DEFAULT_CERT_KEY_SIZE = 2048;
    static final Period DEFAULT_CERT_VALIDITY = Period.ofYears(5);
    static final X500Principal DEFAULT_CA_NAME = new X500Principal("CN=Elasticsearch HTTP CA");
    static final int DEFAULT_CA_KEY_SIZE = DEFAULT_CERT_KEY_SIZE;
    static final Period DEFAULT_CA_VALIDITY = DEFAULT_CERT_VALIDITY;
    private static final String ES_README_CSR = "es-readme-csr.txt";
    private static final String ES_YML_CSR = "es-sample-csr.yml";
    private static final String ES_README_P12 = "es-readme-p12.txt";
    private static final String ES_YML_P12 = "es-sample-p12.yml";
    private static final String CA_README_P12 = "ca-readme-p12.txt";
    private static final String KIBANA_README = "kibana-readme.txt";
    private static final String KIBANA_YML = "kibana-sample.yml";