default Object getUserToken(HttpRoute route, HttpRequest request, HttpContext context) {
        return getUserToken(route, context);
    }
The token object returned by this method is expected to uniquely
identify the current user if the context is user specific or to be
{@code null} if it is not.

@param route HTTP route
@param request HTTP request
@param context the execution context

@return user token that uniquely identifies the user or
{@code null} if the context is not user specific.

@since 5.2
httpclient5/src/main/java/org/apache/hc/client5/http/UserTokenHandler.java