Example Middleware next format

NextMiddleware.fs

type GiraffeMiddleware (next          : RequestDelegate,
                        handler       : HttpHandler,
                        loggerFactory : ILoggerFactory) =

member __.Invoke (ctx : HttpContext) =
        task {
            let finalNext = (fun ctx -> task { Some ctx } )
            let! result = handler finalNext ctx

            if (result.IsNone) then
                return! next.Invoke ctx
        }