Passing Additional Parameter to the redirect_uri when authenticating using OAuth

I am trying to authenticate a third party tool with VSO.During perform OAuth VSO validates the URI configured in the application with the redirect_uri parameter that is passed in the authorize URL to be same otherwise it states that the request is bad (error 404 is displayed). Could somebody tell me how to pass a custom parameter in the redirect_URL. While configuring the application system is not letting me enter a custom query string parameter.Any help would be much appreciated.