private static String encodeSingleParameter(final String key, final String value, final String encoding) {
        return EncodingUtils.urlEncode(key, encoding) + '=' + EncodingUtils.urlEncode(value, encoding);
    }
Default flow execution key parameter name, {@value}.
Same as that used by {@link DefaultFlowUrlHandler}.
core/cas-server-core-webflow-api/src/main/java/org/apereo/cas/web/flow/CasDefaultFlowUrlHandler.java