The important thing here is that you're simulating a browser POST event. Don't worry about text boxes and other visual form elements, your goal is to generate a HTTP POST request with the appropriate key-value pairs.
Your first step is to look through the HTML of the page you're pretend to be and figure out the names of the user id and password form elements. So, let's say for example that they're called "txtUsername" and "txtPassword" respectively, then the post arguments that the browser (or user-agent) will be sending up in its POST request will besomething like:
txtUsername=fflintstone&txtPassword=ilikerocks
As a background to this, you might like to do a little research on how HTTP works. But I'll leave that to you.
The other important thing is to figure out what URL it posts this login request to. Normally, this is whatever appears in the address bar of the browser when you log in, but it may be something else. You'll need to check the action attribute of the form element so see where it goes.
It may be useful to download a copy of Fiddler2. Yes, weird name, but it's a great web debugging tool that basically acts as a proxy and captures everything going between the browser and the remote host. Once you figure out how to use it, you can then pull apart each request-response to see what's happening. It'll give you the URL being called, the type of the request (usually GET or POST), the request arguments, and the full text of the response.
Now, you want to build your app. You need to build logic which make the correct HTTP requests, pass in the form arguments, and get back the results. Luckily, the System.Net.HttpWebRequest class will help you do just that.
Let's say the login page is at www.hello.org/login.aspx and it expects you to POST the login arguments. So your code might look something like this (obviously, this is very simplified):
Imports System.IO
Imports System.Net
Imports System.Web
Dim uri As String = "http://www.hello.org/login.aspx"
Dim request As HttpWebRequest = DirectCast(WebRequest.Create(uri), HttpWebRequest)
request.Timeout = 10000 ' 10 seconds
request.UserAgent = "FlintstoneFetcher/1.0" ' or whatever
request.Accept = "text/*"
request.Headers.Add("Accept-Language", "en")
request.Method = "POST"
Dim data As Byte() = New ASCIIEncoding().GetBytes("txtUsername=fflintstone&txtPassword=ilikerocks")
request.ContentType = "application/x-www-form-urlencoded"
request.ContentLength = data.Length
Dim postStream As Stream = request.GetRequestStream()
postStream.Write(data, 0, data.Length)
postStream.Close()
Dim webResponse As HttpWebResponse
webResponse = DirectCast(request.GetResponse(), HttpWebResponse)
Dim streamReader As StreamReader = New StreamReader(webResponse.GetResponseStream(), Encoding.GetEncoding(1252))
Dim response As String = streamReader.ReadToEnd()
streamReader.Close()
webResponse.Close()
The response string now contains the full response text from the remote host, and that host should consider you logged in. You may need to do a little extra work if the remote host is trying to set cookies (you'll need to return those cookies). Alternatively, if it expects you to pass integrated authentication on successive pages, you'll need to add credentials to your successive requests, something like:
request.Credentials = New NetworkCredential(theUsername, thePassword)
That should be enough information to get cracking. I would recommend that you modularise your logic for working with HTTP into a class of its own. I've implemented a complex solution that logs into a certain website, navigates to a pre-determined page, parses the html and looks for a daily file to be downloaded in the "invox" and if it exists then downloads it. I set this up as a batch process which runs each morning, saving someone having to do this manually. Hopefully, my experience will benefit you!
