This code isn't rocket science, but it might save you a bit of time. (Though it's not groud breaking, keep in mind that I'm the copyright holder. You're free to use it under the turns of the GPL, which all code I post on my blog is governed by unless stated otherwise). If you have questions, shoot them my way.
Web Form
<%@ Page Language="C#" AutoEventWireup="true"using System;
CodeFile="Default.aspx.cs" Inherits="_Default" %>
<html>
<head><title>IdP-initiated SSO using WIF</title></head>
<body>
<form id="form1" runat="server" action="https://localhost:9031/sp/ACS.saml2">
<input type="text" style="width: 400px" name="RelayState"
value="http://localhost/SpSample/?foo=bar" />
<input type="hidden" name="SAMLResponse" id="SAMLResponse" runat="server" />
<input type="submit"/>
</form>
</body>
</html>
Web Form's Code Behind
using System.Collections.Generic;
using System.IdentityModel.Tokens;
using System.IO;
using System.Security.Cryptography.X509Certificates;
using System.Text;
using System.Xml;
using Microsoft.IdentityModel.Claims;
using Microsoft.IdentityModel.Protocols.WSTrust;
using Microsoft.IdentityModel.SecurityTokenService;
using Microsoft.IdentityModel.Tokens;
using Microsoft.IdentityModel.Tokens.Saml2;
using SecurityTokenTypes = Microsoft.IdentityModel.Tokens.SecurityTokenTypes;
public partial class _Default : System.Web.UI.Page
{
#region Configuration Information
private const int tokenLifetime = 1; // In minutes.
private const string issuer = "localhost:default:idp:entityId";
More Here
Courtesy:http://travisspencer.com/blog/2010/09/idp-initiated-sso-using-wif.html