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/test/java/org/elasticsearch/xpack/security/cli/HttpCertificateCommandTests.java
final int certYears = randomIntBetween(1, 8);
        terminal.addTextInput(certYears + "y"); 
        terminal.addTextInput("y"); 
        for (int i = 0; i < numberCerts; i++) {
            if (i != 0) {
                terminal.addTextInput(randomBoolean() ? "y" : ""); 
            }
            
            terminal.addTextInput(certNames[i]);
            
            terminal.addTextInput(hostNames[i]); 
            terminal.addTextInput(""); 
            terminal.addTextInput(randomBoolean() ? "y" : ""); 
            
            terminal.addTextInput(""); 
            terminal.addTextInput(randomBoolean() ? "y" : ""); 
            terminal.addTextInput(randomBoolean() ? "n" : ""); 
        }
        terminal.addTextInput("n"); 
        final String password = randomPassword(false);
        
        if (randomBoolean()) {
            String wrongPassword = randomAlphaOfLengthBetween(8, 20);
            terminal.addTextInput(wrongPassword);
            terminal.addTextInput("__" + wrongPassword);
        }
        terminal.addSecretInput(password);
        if ("".equals(password) == false) {
            terminal.addSecretInput(password);
        }