ASP.NET Generic Handlers & Session

Implement the System.Web.SessionState.IRequiresSessionState interface:

public class Handler : IHttpHandler, System.Web.SessionState.IRequiresSessionState 
{   
  public void ProcessRequest(HttpContext context)  
  {      
    context.Session["StackOverflow"] = "overflowing";      
    context.Response.Redirect("~/AnotherPage.aspx");      
  }

}

You can use this:

public class Handler : 
    IHttpHandler, 
    System.Web.SessionState.IReadOnlySessionState

Generic handlers must implement the IReadOnlySessionState interface to access session variables. If you also need to write session variables, implement IRequiresSessionState.