how to enable session in asp.net api

The small issue about enable the session on the API call is you need to add to all the calls on teh API, on WebForms you can add only on teh call you need use the session. Fro me the most easy way is enable on the Global.asax.

protected void Application_PostAuthenticateRequest(object sender, EventArgs e)
        {
            //implement session on api calls
                HttpContext.Current.SetSessionStateBehavior(System.Web.SessionState.SessionStateBehavior.Required);
        }

With this action you already can get a session from the API.