Your code will unfortunately not work the way you have it constructed right now. in your login.php form, you need to assign the username and password to its respective values. Normally there is a textbox for both in a browser. We need to get these textbox names to add the values and then similate a click event of the login button.
I've tried to get to your page with the url supplied, there is nothing available on the browser form.
The first part of .navigate is correct up to the end of login.php. after that we need to assign these values to be able to login. please show the code you are using in your login.php page.
For Each ctrl As Control In Me.Controls("pnlMainPanel").Controls
If ctrl.GetType Is GetType(System.Windows.Forms.Panel) Then
For Each subCtrl As Control In ctrl.Controls
If subCtrl.GetType Is GetType(System.Windows.Forms.TextBox) Then
If subCtrl.GetType Is ...