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
import static org.hamcrest.Matchers.notNullValue;
import static org.hamcrest.Matchers.oneOf;
public class HttpCertificateCommandTests extends ESTestCase {
    private static final String CA_PASSWORD = "ca-password";
    private FileSystem jimfs;
    private Path testRoot;
    @Before
    public void createTestDir() throws Exception {
        Configuration conf = Configuration.unix().toBuilder().setAttributeViews("posix").build();
        jimfs = Jimfs.newFileSystem(conf);
        testRoot = jimfs.getPath(getClass().getSimpleName() + "-" + getTestName());
        IOUtils.rm(testRoot);
        Files.createDirectories(testRoot);
    }
    @BeforeClass
    public static void muteInFips() {
        assumeFalse("Can't run in a FIPS JVM", inFipsJvm());
    }
    public void testGenerateSingleCertificateSigningRequest() throws Exception {
        final Path outFile = testRoot.resolve("csr.zip").toAbsolutePath();
        final List<String> hostNames = randomHostNames();
        final List<String> ipAddresses = randomIpAddresses();
        final String certificateName = hostNames.get(0);
        final HttpCertificateCommand command = new PathAwareHttpCertificateCommand(outFile);
        final MockTerminal terminal = MockTerminal.create();
        terminal.addTextInput("y"); 
        terminal.addTextInput(randomBoolean() ? "n" : ""); 
        
        hostNames.forEach(terminal::addTextInput);
        terminal.addTextInput("");