DotNetOpenAuth 4.3 and Google - OpenID 2.0 + OAuth 1.0 deprecated

Question

If you want to cut to the chase, the question is: what is the best/official way to use DotNetOpenAuth with Google in asp.net mvc 5?

About a year ago, I used OAuth (D

Answer 1

This is how you use DotnetOpenAuth with Google/OAuth2.

First, reference the DotnetOpenAuth.Ultimate package from Nuget.

Then create a provider class and the profile model class

public class GoogleClient : WebServerClient
{
    private static readonly AuthorizationServerDescription GoogleDescription = 
        new AuthorizationServerDescription
    {
        TokenEndpoint = new Uri( "https://accounts.google.com/o/oauth2/token" ),
        AuthorizationEndpoint = new Uri( "https://accounts.google.com/o/oauth2/auth" ),
        ProtocolVersion = ProtocolVersion.V20
    };

    public const string ProfileEndpoint = "https://www.googleapis.com/oauth2/v1/userinfo";

    public const string ProfileScope = "https://www.googleapis.com/auth/userinfo.profile";
    public const string EmailScope = "https://www.googleapis.com/auth/userinfo.email";

    public GoogleClient()
        : base( GoogleDescription )
    {
    }
}

public class GoogleProfileAPI
{
    public string email { get; set; }

    private static DataContractJsonSerializer jsonSerializer = 
        new DataContractJsonSerializer( typeof( GoogleProfileAPI ) );

    public static GoogleProfileAPI Deserialize( Stream jsonStream )
    {
        try
        {
            if ( jsonStream == null )
            {
                throw new ArgumentNullException( "jsonStream" );
            }

            return (GoogleProfileAPI)jsonSerializer.ReadObject( jsonStream );
        }
        catch ( Exception ex )
        {
            return new GoogleProfileAPI();
        }
    }
}

Then, in your login page (login controller) have this code:

    private static readonly GoogleClient googleClient = new GoogleClient
    {
        ClientIdentifier = "client_id",
        ClientCredentialApplicator = ClientCredentialApplicator.PostParameter( "client_secret" )
    };

        // Page_Load of login page if WebForms
        // Login action of the Account controller if MVC 

        IAuthorizationState authorization = googleClient.ProcessUserAuthorization();
        if ( authorization == null )
        {
            // Kick off authorization request
            // Google will redirect back here
            Uri uri = new Uri( "http://your.application.address/login" );
            googleClient.RequestUserAuthorization( returnTo: uri, 
                scope: new[] { GoogleClient.ProfileScope, GoogleClient.EmailScope } );
        }
        else
        {
            // authorization. we have the token and 
            // we just go to profile APIs to get email (and possibly other data)
            var request =
                WebRequest.Create(
                    string.Format( "{0}?access_token={1}", 
                    GoogleClient.ProfileEndpoint, 
                    Uri.EscapeDataString( authorization.AccessToken ) ) );
            using ( var response = request.GetResponse() )
            {
                using ( var responseStream = response.GetResponseStream() )
                {
                    var profile = GoogleProfileAPI.Deserialize( responseStream );
                    if ( profile != null &&
                        !string.IsNullOrEmpty( profile.email ) )
                        FormsAuthentication.RedirectFromLoginPage( profile.email, false );
                }
            }
        }