private static KeyDescriptor buildKeyDescriptorElement(UsageType type, @Nullable KeyInfo key) {
        final KeyDescriptor descriptor = build(KeyDescriptor.DEFAULT_ELEMENT_NAME);
        descriptor.setUse(type);
        descriptor.setKeyInfo(key);
        return descriptor;
    }
A service which returns the SAML metadata in response to a user request.
saml/src/main/java/com/linecorp/armeria/server/saml/SamlMetadataServiceFunction.java