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
transportCert = parseCertificateFromPem(transportCertPem, terminal);
        } else {
            
            try {
                transportAddresses = List.of();
                
                final KeyPair transportCaKeyPair = CertGenUtils.generateKeyPair(TRANSPORT_CA_KEY_SIZE);
                final PrivateKey transportCaKey = transportCaKeyPair.getPrivate();
                transportCaCert = CertGenUtils.generateSignedCertificate(
                    caPrincipal,
                    null,
                    transportCaKeyPair,
                    null,
                    null,
                    true,
                    TRANSPORT_CA_CERTIFICATE_DAYS,
                    SIGNATURE_ALGORITHM
                );
                
                final KeyPair transportKeyPair = CertGenUtils.generateKeyPair(TRANSPORT_KEY_SIZE);
                transportKey = transportKeyPair.getPrivate();
                transportCert = CertGenUtils.generateSignedCertificate(
                    certificatePrincipal,
                    null, 
                    transportKeyPair,
                    transportCaCert,
                    transportCaKey,
                    false,
                    TRANSPORT_CERTIFICATE_DAYS,
                    SIGNATURE_ALGORITHM