Redirecting with credentials to another website - asp.net

Question

I have two websites A and B. On A I have the login option and if the user is authenticated I need to send it to B with same credentials. I have access to the code of both websites. My first approach was trying to log the user on A and figure out how could I make a Post to a action method on a controller on B(this is a recurrent question here in stackoverflow) I found this website and I don't know if it is useful: http://www.codeproject.com/Articles/833007/Redirect-and-POST-in-ASP-NET-MVC. My second approach is putting all the data that I wanted to submit to B in Browser Session, call a Redirect to B and then in a method("GET") try to read all that data and check if I can proceed with the logic on B.
I want to know which is the best approach to make this happen, and also if the later is wrong or not.
I have this code on my website A:
[HttpPost]
public ActionResult Login(LoginModel user)
{
//hardcoding InternalUser
user.AccountType = ((int)AccountTypeEnum.Internal).ToString();
var validator = new LoginModelValidator();
var result = validator.Validate(user);
if (!result.IsValid)
{
return View((LoginModelDecorator) user);
}
var service = new AuthenticationServiceAgent(user.Username, user.Password);
var securityService = new SecurityServiceAgent(service.GeToken());
var state = securityService.ProcessAccount(service.GeToken() != null, user.Username);
if (state == (int)UserAccessEnum.Processed)
{
var type = securityService.GetAccountTypeByUser(user.Username);
//CHeck user type
var accountType = Enum.GetName(typeof(AccountTypeEnum), int.Parse(user.AccountType));
var types = type.Split(',').Select(n => n.Split(':')[0]).ToList();
var containsTheUserType = user.AccountType == "1"
? types.Contains("XXX") || types.Contains(accountType)
: types.Contains(accountType);
if (containsTheUserType)
{
//var cPrincipal = service.GetClaims();
var claims = securityService.GetIdentity().Select(claim => new Claim(claim.ClaimType, claim.Value)).ToList();
if (claims.Count != 0)
{
var cPrincipal = new ClaimsPrincipal(new ClaimsIdentity(claims, "Custom"));
type.Split(',')
.ToList()
.ForEach(
ty =>
cPrincipal.Identities.First()
.AddClaim(new Claim("http://claims/custom/accounttype", ty)));
var token = new SessionSecurityToken(cPrincipal)
{
IsReferenceMode = true
};
FederatedAuthentication.WSFederationAuthenticationModule.SetPrincipalAndWriteSessionToken(
token, true);
Session["SEC_TOKEN"] = service.GeToken();
//Do I need to post?: SecurityToken, types and claims
//here is where I am redirecting the user
return Redirect("http://localhost:12345/Account/Login");
}
ModelState.AddModelError("LoginError", "Invalid Username or Password!");
}
ModelState.AddModelError("AccountTypeError", "You don't have access");
}
switch (state)
{
case (int)UserAccessEnum.BlockedAccount:
ModelState.AddModelError("StateError", "Your account is Blocked");
break;
case (int)UserAccessEnum.ChangePassword:
ModelState.AddModelError("StateError", "You need to change your password");
break;
case (int)UserAccessEnum.NoProcessed:
ModelState.AddModelError("StateError", "Error, please contact the system administrator");
break;
}
return View((LoginModelDecorator) user);
}
In my website B:
public ActionResult Login()
{
List<Claim> claims = //I need to get the claims from somewhere SESSION?
var type = //type used in the other Loging method
var securityToken = //securityToken used on the other Login method
if (claims.Count != 0)
{
var cPrincipal = new ClaimsPrincipal(new ClaimsIdentity(claims, "Custom"));
type.Split(',')
.ToList()
.ForEach(
ty =>
cPrincipal.Identities.First()
.AddClaim(new Claim("http://claims/custom/accounttype", ty)));
var token = new SessionSecurityToken(cPrincipal)
{
IsReferenceMode = true
};
FederatedAuthentication.WSFederationAuthenticationModule.SetPrincipalAndWriteSessionToken(
token, true);
Session["SEC_TOKEN"] = securityToken;
return RedirectToAction("Index", "Home");
}
return null;
}
Any idea of how to complete the gaps that I have?