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
assertThat(csrPem.getType(), is(expectedType));
        return factory.apply(csrPem.getContent());
    }
    private void writeDummyKeystore(Path path, String type) throws GeneralSecurityException, IOException {
        Files.deleteIfExists(path);
        KeyStore ks = KeyStore.getInstance(type);
        ks.load(null);
        if (randomBoolean()) {
            final X509Certificate cert = CertParsingUtils.readX509Certificate(getDataPath("ca.crt"));
            ks.setCertificateEntry(randomAlphaOfLength(4), cert);
        }
        try (OutputStream out = Files.newOutputStream(path)) {
            ks.store(out, randomAlphaOfLength(8).toCharArray());
        }
    }
    /**
     * A special version of {@link HttpCertificateCommand} that can resolve input strings back to JIMFS paths
     */
    private class PathAwareHttpCertificateCommand extends HttpCertificateCommand {
        final Map<String, Path> paths;
        PathAwareHttpCertificateCommand(Path... configuredPaths) {
            paths = Stream.of(configuredPaths).collect(Collectors.toUnmodifiableMap(Path::toString, Function.identity()));
        }
        @Override
        protected Path resolvePath(String name) {
            return Optional.ofNullable(this.paths.get(name)).orElseGet(() -> super.resolvePath(name));
        }
    }
}