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
assert entry.isDirectory() == false;
            zip.putNextEntry(entry);
        }
        @Override
        public void write(int b) throws IOException {
            zip.write(b);
        }
        @Override
        public void write(byte[] b) throws IOException {
            zip.write(b);
        }
        @Override
        public void write(byte[] b, int off, int len) throws IOException {
            zip.write(b, off, len);
        }
        @Override
        public void flush() throws IOException {
            zip.flush();
        }
        @Override
        public void close() throws IOException {
            zip.closeEntry();
        }
    }
    
    OptionParser getParser() {
        return parser;
    }
}