public static <T> Key<T> newKey(String keyName) {
        return new Key<>(keyName);
    }
A heterogeneous map of attributes.

<p>Implementation Note: this class is not a proper Map or Collection, in order to encourage callers
to refer to the keys by their literal name.   In the past, finding where a Key was used was difficult,
so this class is somewhat of an experiment to try to make tracking down usage easier.  If it becomes
too onerous to use this, consider making this class extend AbstractMap.
zuul-core/src/main/java/com/netflix/zuul/Attrs.java