Send async HTTP POST request

post.fs

open System.Net
open System.IO

let makePostRequest (url : string) (requestBody : string) = 
    let req = WebRequest.CreateHttp url
    req.CookieContainer <- new CookieContainer()
    req.Method <- "POST"
    req.ProtocolVersion <- HttpVersion.Version10
    let postBytes = requestBody |> System.Text.Encoding.ASCII.GetBytes
    req.ContentLength <- postBytes.LongLength
    req.ContentType <- "application/xml; charset=utf-8"
    async{
        use! reqStream = req.GetRequestStreamAsync() |> Async.AwaitTask
        do! reqStream.WriteAsync(postBytes, 0, postBytes.Length) |> Async.AwaitIAsyncResult |> Async.Ignore
        reqStream.Close()
        use! res = req.AsyncGetResponse() 
        use stream = res.GetResponseStream()
        use reader = new StreamReader(stream)
        let! rdata = reader.ReadToEndAsync() |> Async.AwaitTask        
        return rdata
    }