private static boolean hasJsonPropertyAnnotation(Field f) {
        for (Field g : f.getType().getDeclaredFields()) {
            g.setAccessible(true);
            if (g.getAnnotation(JsonProperty.class) != null) {
                return true;
            }
        }
        return false;
    }
Get a claim by name.

@param token token to retrieve claim from
@param claim the claim (field key)
@return string representation of claim
plugins/keycloak-oauth-policy/src/main/java/io/apiman/plugins/keycloak_oauth_policy/ClaimLookup.java