How to use DotNetOpenAuth to login to websites?

问题:

I want to do is, if the users are logged into gmail and if they go to my website they automatically get logged in.

I am doing it in the following way... maybe there is a better way of doing it.

In my website I have a place for uses to give their gmail address so my website knows gamil address of the registered user.

So when they go to my website I want to know whether they are logged into gmail and what is their gmail address.

How should I find this information using DotNetOpenAuth?

I found following code from the web and it is authenticating the user. But i have to press the button and go to gmail login every time. if the user is already using gmail I don’t have to ask the user for login i can use it. How do i modify this code to achieve that?

static string openidurl = "https://www.google.com/accounts/o8/id";
protected void Page_Load(object sender, EventArgs e)
{
    //The Response
     OpenIdRelyingParty openid = new OpenIdRelyingParty();

     var response = openid.GetResponse();
     if (response != null)
     {
             switch (response.Status)
             {
                 case AuthenticationStatus.Authenticated:

                 var fetch = response.GetExtension<FetchResponse>();
                 string email = ""; 
                 if (fetch != null)
                 {
                     email = fetch.GetAttributeValue(WellKnownAttributes.Contact.Email);
                 }  
                break;
              }
    }
}
protected void Button1_Click(object sender, EventArgs e)
{
    using (OpenIdRelyingParty openid = new OpenIdRelyingParty())
    {
        IAuthenticationRequest request = openid.CreateRequest(openidurl);

        var fetch = new FetchRequest();
        fetch.Attributes.AddRequired(WellKnownAttributes.Contact.Email);
        request.AddExtension(fetch);

        // Send your visitor to their Provider for authentication.
        request.RedirectToProvider();
    }
}

回答1:

It sounds like what you're asking for is "single-sign-on", where a visitor to your site who is already logged into Google is immediately logged into your site when they first visit it, rather than after clicking a "Google Login" button on your site.

The short answer is you can't do this. The longer answer is that you can get close.

The first and hard restriction is that first-time visitors to your site will never get automatically signed in, because Google and the user don't yet trust your site. Every user has to explicitly log in once, with Google asking the user "do you want to log into this site and remember this choice?" If they say yes, then in the future when the user is already logged into Google and visits your site, they can click the Google Login button on your site and they'll never see Google -- they'll just be immediately logged into your site.

So the next question is how do you remove the requirement on the user to click "google Login". You can accomplish this by when an unauthenticated user visits your site, you can immediately redirect them to your log in page, which will immediately initiate the "Google Login" flow (the OpenIdRelyingParty.CreateRequest(google).RedirectToProvider() call), using "immediate mode". This will fail if the user isn't logged into Google and trust your site, but the impact will be the user won't see a Google login screen if they do trust your site, but will rather be immediately logged in.

回答2:

You might find my answer useful: What OpenID solution is really used by Stack Overflow?

I've also made a simple blog post about it: http://codesprout.blogspot.com/2011/03/using-dotnetopenauth-to-create-simple.html

My examples are with MyOpenID, but gmail should work the same way. The OpenID provider basically takes care of the log in, including the case when they're already logged in with the provider.

Update:
In an ASP.NET (in this case ASP.NET MVC) application you would create a cookie when the user is successfully logged in and you would check the cookie to determine if the user is logged in. As I said, please see the links above for detailed code examples and an explanation of how it all works. Here are two code samples from the Controller where I demonstrate how to check if the user is logged in:

// **************************************
// URL: /User/LogIn
// **************************************
public ActionResult LogIn()
{
    if (User.Identity.IsAuthenticated) // <--- CHECKS IF THE USER IS LOGGED IN
    {
        return RedirectToAction("Profile", "User");
    }

    Identifier openID;
    if (Identifier.TryParse(Request.QueryString["dnoa.userSuppliedIdentifier"], out openID))
    {
        return LogIn(new User { OpenID = openID }, Request.QueryString["ReturnUrl"]);
    }
    else
    {
        return View();
    }
}

[HttpPost]
public ActionResult LogIn(User model, string returnUrl)
{
    string openID = ModelState.IsValid?model.OpenID:Request.Form["openid_identifier"];

    if (User.Identity.IsAuthenticated)//<--- CHECKS IF THE USER IS LOGGED IN
    {
        return RedirectToAction("Profile", "User");
    }
    else if (!string.IsNullOrEmpty(openID))
    {
        return Authenticate(openID, returnUrl);
    }
    else if(ModelState.IsValid)
    {
        ModelState.AddModelError("error", "The OpenID field is required.");
    }

    // If we got this far, something failed, redisplay form
    return View(model);
}