protected static String getFirstSpecifiedKeyID(final JWKMatcher jwkMatcher) {

		Set<String> keyIDs = jwkMatcher.getKeyIDs();

		if (keyIDs == null || keyIDs.isEmpty()) {
			return null;
		}

		for (String id: keyIDs) {
			if (id != null) {
				return id;
			}
		}
		return null; // No kid in matcher
	}