Outlook365 supports access via IMAP, POP3 and SMTP protocols. Below you can find the configuration settings for all protocols.

Latest Office 365 version

For latest Office 365 after the service upgrade, use the following settings:

IMAP

Server: outlook.office365.com
SSL: true-implicit, true-explicit (StartTLS)
Port: 993 (default), 143 (default)
User: pat@domain.onmicrosoft.com or pat@your-domain.com

POP3

Server: outlook.office365.com
SSL: true-implicit, true-explicit (StartTLS)
Port: 995 (default), 110 (default)
User: pat@domain.onmicrosoft.com or pat@your-domain.com

SMTP

Server: smtp.office365.com
SSL: true-explicit (StartTLS)
Port: 587(default)
User: pat@domain.onmicrosoft.com or pat@your-domain.com

IMAP and POP3 servers allow both: implicit/TLS SSL and explicit SSL/TLS, so you can ConnectSSL method -or- Connect and StartTLS.

SMTP server requires explicit SSL – use Connect and StartTLS method.

// C#

using (Imap client = new Imap())
{
    client.ConnectSSL("outlook.office365.com");
    client.UseBestLogin("user@domain.onmicrosoft.com", "password");
    ...
}

using (Pop3 client = new Pop3())
{
    client.ConnectSSL("outlook.office365.com");
    client.UseBestLogin("user@domain.onmicrosoft.com", "password");
    ...
}

using (Smtp client = new Smtp ())
{
    client.Connect("smtp.office365.com");
    client.StartTLS();

    client.UseBestLogin("user@domain.onmicrosoft.com", "password");
    ...
}

' VB.NET

Using client As New Imap()
	client.ConnectSSL("outlook.office365.com")
	client.UseBestLogin("user@domain.onmicrosoft.com", "password")
	...
End Using

Using client As New Pop3()
	client.ConnectSSL("outlook.office365.com")		
	client.UseBestLogin("user@domain.onmicrosoft.com", "password")
	...
End Using

Using client As New Smtp()
	client.Connect("smtp.office365.com")
	client.StartTLS()

	client.UseBestLogin("user@domain.onmicrosoft.com", "password")
	...
End Using

Office 365 pre-upgrade

For latest Office 365 pre-upgrade, use the following settings:

On the main screen go to “Options” / “See All Options…”:

Now click the “Settings for POP, IMAP, and SMTP access…” link:

You can find POP, SMTP and IMAP server addresses and settings on the popup window:

Office365 uses default ports for IMAP, POP3 and SMTP protocols. That means that you don’t need to remember port numbers, as Mail.dll .NET email component is going to use correct port numbers by default.

IMAP

Server: podXXXX.outlook.com
SSL: true-implicit
Port: 993 (default)
User: pat@domain.onmicrosoft.com or pat@your-domain.com

POP3

Server: podXXXX.outlook.com
SSL: true-implicit
Port: 995 (default)
User: pat@domain.onmicrosoft.com or pat@your-domain.com

SMTP

Server: podXXXX.outlook.com
SSL: true-explicit
Port: 587 (default)
User: pat@domain.onmicrosoft.com or pat@your-domain.com

IMAP and POP3 servers use implicit SSL – use ConnectSSL method. SMTP server requires explicit SSL – use Connect and StartTLS method.

// C#

using (Imap client = new Imap())
{
    client.ConnectSSL("podXXXX.outlook.com");
    client.UseBestLogin("user@domain.onmicrosoft.com", "password");
    ...
}

using (Pop3 client = new Pop3())
{
    client.ConnectSSL("podXXXX.outlook.com");
    client.UseBestLogin("user@domain.onmicrosoft.com", "password");
    ...
}

using (Smtp client = new Smtp ())
{
    client.Connect("podXXXX.outlook.com");
    client.StartTLS();

    client.UseBestLogin("user@domain.onmicrosoft.com", "password");
    ...
}

' VB.NET

Using client As New Imap()
	client.ConnectSSL("podXXXX.outlook.com")
	client.UseBestLogin("user@domain.onmicrosoft.com", "password")
	...
End Using

Using client As New Pop3()
	client.ConnectSSL("podXXXX.outlook.com")		
	client.UseBestLogin("user@domain.onmicrosoft.com", "password")
	...
End Using

Using client As New Smtp()
	client.Connect("podXXXX.outlook.com")
	client.StartTLS()

	client.UseBestLogin("user@domain.onmicrosoft.com", "password")
	...
End Using

You can find more details about using implicit and explicit SSL or TLS with email protocols:

• Using SSL with IMAP
• Using SSL with POP3
• Using SSL with SMTP

This article describes how to receive email messages using Mail.dll .NET email library.

Sending email is built into .NET, so there’s no need for 3rd party library, however Mail.dll is much easier to use than SmtpClient,
and much more powerful. Receiving is a bit more complicated. It does require a 3rd party library.

There are two standard protocols for receiving emails IMAP (Internet Message Access Protocol) and POP3 (Post Office Protocol).
Without getting in to much details IMAP is better and offers more features when receiving emails (you can find a detailed IMAP vs POP3 comparison here). We’ll use Imap class to work with this protocol.

As a prerequisite you need to add reference to Mail.dll to your project and import following namespaces:

// C#

using Limilabs.Mail;
using Limilabs.Client.IMAP;

' VB

Imports Limilabs.Mail
Imports Limilabs.Client.IMAP

First thing you need to do is to connect to your IMAP email server. Most servers today require SSL or TLS. We’ll use ConnectSSL(string host) to connect and establish secure channel. This method makes sure correct SSL/TLS versions are used and server certificate are valid:

// C#

using (Imap imap = new Imap ())
{
    imap.ConnectSSL("imap.example.com");  
    imap.UseBestLogin("user@example.com", "password");

' VB

Using imap As New Imap()
    imap.ConnectSSL("imap.example.com")
    imap.UseBestLogin("user@example.com", "password")

Next step is to select a folder which we want to access and download unique ids (UIDs) of email messages. In this example we’ll search and receive unseen emails from INBOX folder.

// C#

imap.SelectInbox();
List<long> uids = imap.Search(Flag.Unseen);

' VB

imap.SelectInbox()
Dim uids As List(Of Long) = imap.Search(Flag.Unseen)

Finally we need to receive and process those emails. On the server emails are stored in MIME format. GetMessageByUID method receives emails as a raw byte array and MailBuilder class can be used to parse it:

// C#

foreach (long uid in uids)
{
    var eml = imap.GetMessageByUID(uid)
    IMail email = new MailBuilder().CreateFromEml(eml);

    Console.WriteLine(email.Subject);
    Console.WriteLine(email.Text);
}

' VB

For Each uid As Long In uids
{
    Dim eml = imap.GetMessageByUID(uid)
    Dim email As IMail = builder.CreateFromEml(eml)

    Console.WriteLine(email.Subject)
    Console.WriteLine(email.Text)
}

At that point you can also access attachments or From and To fields.

Here are the full samples that receive emails in both C# and VB .NET:

// C#

using Limilabs.Mail;
using Limilabs.Client.IMAP;

class Program
{
    static void Main(string[] args)
    {
        using(Imap imap = new Imap())
        {
            imap.ConnectSSL("imap.example.com"); 
            imap.UseBestLogin("user", "password");

            imap.SelectInbox();
            List<long> uids = imap.Search(Flag.Unseen);

            foreach (long uid in uids)
            {
                var eml = imap.GetMessageByUID(uid);
                IMail email = new MailBuilder()
                    .CreateFromEml(eml);

                Console.WriteLine(email.Subject);
                Console.WriteLine(email.Text);
            }
            imap.Close();
        }
    }
};

' VB.NET

Imports Limilabs.Mail
Imports Limilabs.Client.IMAP

Public Module Module1
    Public Sub Main(ByVal args As String())
        Using imap As New Imap()
            imap.ConnectSSL("imap.example.com")
            imap.UseBestLogin("user", "password")

            imap.SelectInbox()
            Dim uids As List(Of Long) = imap.Search(Flag.Unseen)

            For Each uid As Long In uids
                Dim eml = imap.GetMessageByUID(uid)
                Dim email As IMail = New MailBuilder() _
                    .CreateFromEml(eml)

                Console.WriteLine(email.Subject)
                Console.WriteLine(email.Text)
            Next
            imap.Close()
        End Using
    End Sub
End Module

OAuth is an open protocol to allow secure API authorization in a simple and standard method from desktop and web applications.

This article describes using OAuth 2.0 to access Gmail IMAP and SMTP servers using .NET IMAP component in installed applications scenario. You can also use OAuth 2.0 for web applications.

Google.Apis

Use Nuget to download “Google.Apis.Auth” package.

Import namespaces:

// c#

using Google.Apis.Auth.OAuth2;
using Google.Apis.Auth.OAuth2.Flows;
using Google.Apis.Auth.OAuth2.Requests;
using Google.Apis.Auth.OAuth2.Responses;

using Limilabs.Client.Authentication.Google;

using Limilabs.Client.IMAP;

' VB.NET 

Imports Google.Apis.Auth.OAuth2
Imports Google.Apis.Auth.OAuth2.Flows
Imports Google.Apis.Auth.OAuth2.Requests
Imports Google.Apis.Auth.OAuth2.Responses

Imports Limilabs.Client.Authentication.Google

Imports Limilabs.Client.IMAP

Register Application

Before you can use OAuth 2.0, you must register your application using the Google Developers Console.

At least product name must be specified:

Now create credentials:

After you’ve registered, copy the “Client ID” and “Client secret” values, which you’ll need later:

Now we can define clientID, clientSecret and scope variables, as well as Google OAuth 2.0 server addresses. Scope basically specifies what services we want to have access to. In our case it is user’s email address and IMAP/SMTP access:

// c#

string clientID = "XXX.apps.googleusercontent.com";
string clientSecret = "IxBs0g5sdaSDUz4Ea7Ix-Ua";

var clientSecrets = new ClientSecrets
{
    ClientId = clientID,
    ClientSecret = clientSecret
};

var credential = new GoogleAuthorizationCodeFlow(new GoogleAuthorizationCodeFlow.Initializer
{
    ClientSecrets = clientSecrets,
    Scopes = new[] { GoogleScope.ImapAndSmtp.Name, GoogleScope.EmailScope.Name}
});

' VB.NET 

Dim clientID As String = "XXX.apps.googleusercontent.com"
Dim clientSecret As String = "IxBs0g5sdaSDUz4Ea7Ix-Ua"

Dim clientSecrets = New ClientSecrets() With { _
	Key .ClientId = clientID, _
	Key .ClientSecret = clientSecret _
}

Dim credential = New GoogleAuthorizationCodeFlow(New GoogleAuthorizationCodeFlow.Initializer() With { _
	Key .ClientSecrets = clientSecrets, _
	Key .Scopes = New () {GoogleScope.ImapAndSmtp.Name, GoogleScope.EmailScope.Name} _
})

Turn on Google+ API

Remember to turn on Google+ API:

It is required to obtain email address of the user.

Obtain an OAuth 2.0 access token

Now we’ll create authorization url:

AuthorizationCodeRequestUrl url = credential.CreateAuthorizationCodeRequest("urn:ietf:wg:oauth:2.0:oob");

Process.Start(url.Build().ToString());

' VB.NET 

Dim url As AuthorizationCodeRequestUrl = credential.CreateAuthorizationCodeRequest("urn:ietf:wg:oauth:2.0:oob")

Process.Start(url.Build().ToString())

We are using Process.Start here, but you can also embed WebBrowser control in your application.

At this point user is redirected to Google to authorize the access:

After this step user is presented a code that needs to be pasted to your application:

Please note that this code also appears in the title of the browser:

• It is possible to monitor processes on your machine and act automatically when it is there.
• If you use embedded WebBrowser control in your application, you can monitor the HTML document title after any redirect.

Following is a code that reads this code and contacts Google to exchange it for a refresh-token and an access-token:

string authCode = Console.ReadLine();

TokenResponse token = await credential.ExchangeCodeForTokenAsync("", authCode, "urn:ietf:wg:oauth:2.0:oob", CancellationToken.None);

string accessToken = token.AccessToken;

' VB.NET 

Dim authCode As String = Console.ReadLine()

Dim token As TokenResponse = Await credential.ExchangeCodeForTokenAsync("", authCode, "urn:ietf:wg:oauth:2.0:oob", CancellationToken.None)

Dim accessToken As String = token.AccessToken

An access token is usually valid for a maximum of one hour, and allows you to access the user’s data. You also received a refresh token. A refresh token can be used to request a new access token once the previous expired.

Access IMAP/SMTP server

Finally we’ll ask Google for user’s email and use LoginOAUTH2 method to access Gmail’s IMAP server:

// c#

GoogleApi api = new GoogleApi(accessToken);
string user = api.GetEmailPlus();

using (Imap imap = new Imap())
{
    imap.ConnectSSL("imap.gmail.com");
    imap.LoginOAUTH2(user, accessToken);

    imap.SelectInbox();
    List<long> uids = imap.Search(Flag.Unseen);

    foreach (long uid in uids)
    {
        var eml = imap.GetMessageByUID(uid);
        IMail email = new MailBuilder().CreateFromEml(eml);
        Console.WriteLine(email.Subject);
    }
    imap.Close();
}

' VB.NET 

Dim api As New GoogleApi(accessToken)
Dim user As String = api.GetEmailPlus()

Using imap As New Imap()
	imap.ConnectSSL("imap.gmail.com")
	imap.LoginOAUTH2(user, accessToken)

	imap.SelectInbox()
	Dim uids As List(Of Long) = imap.Search(Flag.Unseen)

	For Each uid As Long In uids
		Dim eml = imap.GetMessageByUID(uid)
		Dim email As IMail = New MailBuilder().CreateFromEml(eml)
		Console.WriteLine(email.Subject)
	Next
	imap.Close()
End Using

Refreshing access token

An access token is usually short lived and valid for a maximum of one hour. The main reason behind this is security and prevention of replay attacks. This means that for long-lived applications you need to refresh the access token.

Your refresh token will be sent only once – don’t loose it!

We recommend storing entire TokenResponse object received from GoogleAuthorizationCodeFlow.ExchangeCodeForTokenAsync method call. This object contains both: refresh token and access token, along with its expiration time.

The process of refreshing access token is simple:

// c#

TokenResponse refreshed = await credential.RefreshTokenAsync("", token.RefreshToken, CancellationToken.None);

' VB.NET 

Dim refreshed As TokenResponse = Await credential.RefreshTokenAsync("", token.RefreshToken, CancellationToken.None)

OAuth is an open protocol to allow secure API authorization in a simple and standard method from desktop and web applications.

This article describes using OAuth 2.0 to access Gmail IMAP and SMTP servers using .NET IMAP component in web application scenario (ASP.NET/ASP.NET MVC). You can also use OAuth 2.0 for installed applications.

Google.Apis

Use Nuget to download “Google.Apis.Auth” package.

Import namespaces:

// c#

using Google.Apis.Auth.OAuth2;
using Google.Apis.Auth.OAuth2.Flows;
using Google.Apis.Auth.OAuth2.Requests;
using Google.Apis.Auth.OAuth2.Responses;

using Limilabs.Client.Authentication.Google;

using Limilabs.Client.IMAP;

' VB.NET 

Imports Google.Apis.Auth.OAuth2
Imports Google.Apis.Auth.OAuth2.Flows
Imports Google.Apis.Auth.OAuth2.Requests
Imports Google.Apis.Auth.OAuth2.Responses

Imports Limilabs.Client.Authentication.Google

Imports Limilabs.Client.IMAP

Register Application

Before you can use OAuth 2.0, you must register your application using the Google Developers Console. After you’ve registered, go to the API Access tab and copy the “Client ID” and “Client secret” values and specify “Redirect URI“, which you’ll need later.

At least product name must be specified:

Now create credentials:

Specify redirect URI:

After you’ve registered, copy the “Client ID” and “Client secret” values, which you’ll need later:

Now we can define clientID, clientSecret, redirect url and scope variables, as well as Google OAuth 2.0 server addresses. Scope basically specifies what services we want to have access to. In our case it is user’s email address and IMAP/SMTP access:

// c#

string clientID = "XXX.apps.googleusercontent.com";
string clientSecret = "IxBs0g5sdaSDUz4Ea7Ix-Ua";
string redirectUri = "http://www.yourdomain.com/oauth2callback";

var clientSecrets = new ClientSecrets
{
    ClientId = clientID,
    ClientSecret = clientSecret
};

var credential = new GoogleAuthorizationCodeFlow(new GoogleAuthorizationCodeFlow.Initializer
{
    ClientSecrets = clientSecrets,
    Scopes = new[] { GoogleScope.ImapAndSmtp.Name, GoogleScope.EmailScope.Name}
});

' VB.NET 

Dim clientID As String = "XXX.apps.googleusercontent.com"
Dim clientSecret As String = "IxBs0g5sdaSDUz4Ea7Ix-Ua"
Dim redirectUri As String = "http://www.yourdomain.com/oauth2callback"

Dim clientSecrets = New ClientSecrets() With { _
	Key .ClientId = clientID, _
	Key .ClientSecret = clientSecret _
}

Dim credential = New GoogleAuthorizationCodeFlow(New GoogleAuthorizationCodeFlow.Initializer() With { _
	Key .ClientSecrets = clientSecrets, _
	Key .Scopes = New () {GoogleScope.ImapAndSmtp.Name, GoogleScope.EmailScope.Name} _
})

Turn on Google+ API

Remember to turn on Google+ API:

It is required to obtain email address of the user.

Obtain an OAuth 2.0 access token

Now we’ll create authorization url:

AuthorizationCodeRequestUrl url = credential.CreateAuthorizationCodeRequest(redirectUri);

' VB.NET 

Dim url As AuthorizationCodeRequestUrl = credential.CreateAuthorizationCodeRequest(redirectUri)

Now we need to redirect the client:

// c#

return new RedirectResult(url.Build().ToString());

' VB.NET 

Return New RedirectResult(url.Build().ToString())

At this point user is redirected to Google to authorize the access:

After this step user is redirected back to your website (http://www.yourdomain.com/oauth2callback), with code request parameter:
http://www.yourdomain.com/oauth2callback?code=4/5Y7M4cARD9hrt0nuKnQa0YgtYMasdbwprRtIIjk4Fus#

// c#

public class OAauth2CallbackController : Controller
{
    public ActionResult Index(string code)
    {
        ...
    }
}

' VB.NET 

Public Class OAauth2CallbackController
    Inherits Controller
    Public Function Index(code As String) As ActionResult
        ...
    End Function
End Class

Following is this callback code. Its purpose is to get a refresh-token and an access-token:

// c#

string authCode = code;

TokenResponse token = await credential.ExchangeCodeForTokenAsync("", authCode, redirectUri, CancellationToken.None);

string accessToken = token.AccessToken;

' VB.NET 

Dim authCode As String = code

Dim token As TokenResponse = Await credential.ExchangeCodeForTokenAsync("", authCode, redirectUri, CancellationToken.None)

Dim accessToken As String = token.AccessToken

An access token is usually valid for a maximum of one hour, and allows you to access the user’s data. You also received a refresh token. A refresh token can be used to request a new access token once the previous expired.

Access IMAP/SMTP server

Finally we’ll ask Google for user’s email and use LoginOAUTH2 method to access Gmail’s IMAP server:

// c#

GoogleApi api = new GoogleApi(accessToken);
string user = api.GetEmailPlus();

using (Imap imap = new Imap())
{
    imap.ConnectSSL("imap.gmail.com");
    imap.LoginOAUTH2(user, accessToken);

    imap.SelectInbox();
    List<long> uids = imap.Search(Flag.Unseen);

    foreach (long uid in uids)
    {
        var eml = imap.GetMessageByUID(uid);
        IMail email = new MailBuilder().CreateFromEml(eml);
        Console.WriteLine(email.Subject);
    }
    imap.Close();
}

' VB.NET 

Dim api As New GoogleApi(accessToken)
Dim user As String = api.GetEmailPlus()

Using imap As New Imap()
	imap.ConnectSSL("imap.gmail.com")
	imap.LoginOAUTH2(user, accessToken)

	imap.SelectInbox()
	Dim uids As List(Of Long) = imap.Search(Flag.Unseen)

	For Each uid As Long In uids
		Dim eml = imap.GetMessageByUID(uid)
		Dim email As IMail = New MailBuilder().CreateFromEml(eml)
		Console.WriteLine(email.Subject)
	Next
	imap.Close()
End Using

Refreshing access token

An access token is usually short lived and valid for a maximum of one hour. The main reason behind this is security and prevention of replay attacks. This means that for long-lived applications you need to refresh the access token.

Your refresh token will be sent only once – don’t loose it!

We recommend storing entire TokenResponse object received from GoogleAuthorizationCodeFlow.ExchangeCodeForTokenAsync method call. This object contains both: refresh token and access token, along with its expiration time.

The process of refreshing access token is simple:

// c#

TokenResponse refreshed = await credential.RefreshTokenAsync("", token.RefreshToken, CancellationToken.None);

' VB.NET 

Dim refreshed As TokenResponse = Await credential.RefreshTokenAsync("", token.RefreshToken, CancellationToken.None)

OAuth is an open protocol to allow secure API authorization in a simple and standard method from desktop and web applications.

This article describes using OAuth 2.0 to access Gmail IMAP and SMTP servers using .NET IMAP component in installed applications scenario. You can also use OAuth 2.0 for web applications.

DotNetOpenAuth

First download the latest version of DotNetOpenAuth – it’s free, open source library that implements OAuth 2.0: http://www.dotnetopenauth.net

Register Application

Before you can use OAuth 2.0, you must register your application using the Google Developers Console.

At least product name must be specified:

Now create credentials:

After you’ve registered, copy the “Client ID” and “Client secret” values, which you’ll need later:

Now we can define clientID, clientSecret and scope variables, as well as Google OAuth 2.0 server addresses. Scope basically specifies what services we want to have access to. In our case it is user’s email address and IMAP/SMTP access:

const string clientID = "12345.apps.googleusercontent.com";
const string clientSecret = "XXXYYY111";

AuthorizationServerDescription server = new AuthorizationServerDescription
    {
        AuthorizationEndpoint = new Uri("https://accounts.google.com/o/oauth2/auth"),
        TokenEndpoint = new Uri("https://accounts.google.com/o/oauth2/token"),
        ProtocolVersion = ProtocolVersion.V20,
    };
List<string> scope = new List<string> 
    { 
        GoogleScope.ImapAndSmtp.Name,
        GoogleScope.EmailScope.Name 
    };

Turn on Google+ API

Remember to turn on Google+ API:

It is required to obtain email address of the user.

Obtain an OAuth 2.0 access token

As we are using installed applications scenario we’ll use NativeApplicationClient class.

Because of a small issue in DotNetOpenAuth we can not use UserAgentClient directly. NativeApplicationClient inherits UserAgentClient and workarounds this issue. You can find the implementation of NativeApplicationClient on the bottom of this article.

NativeApplicationClient consumer = new NativeApplicationClient(server, clientID, clientSecret);
Uri userAuthorizationUri = consumer.RequestUserAuthorization(scope);

Process.Start(userAuthorizationUri.AbsoluteUri);

We are using Process.Start here, but you can also embed WebBrowser control in your application.

At this point user is redirected to Google to authorize the access:

After this step user is presented a code that needs to be pasted to your application:

Please note that this code also appears in the title of the browser:

• It is possible to monitor processes on your machine and act automatically when it is there.
• If you use embedded WebBrowser control in your application, you can monitor the HTML document title after any redirect.

Following is a code that reads this code and contacts Google to exchange it for a refresh-token and an access-token:

string authCode = Console.ReadLine();

consumer.ClientCredentialApplicator = ClientCredentialApplicator.PostParameter(clientSecret);

IAuthorizationState grantedAccess = consumer.ProcessUserAuthorization(authCode);

string accessToken = grantedAccess.AccessToken;

An access token is usually valid for a maximum of one hour, and allows you to access the user’s data. You also received a refresh token. A refresh token can be used to request a new access token once the previous expired.

Access IMAP/SMTP server

Finally we’ll ask Google for user’s email and use LoginOAUTH2 method to access Gmail’s IMAP server:

GoogleApi api = new GoogleApi(accessToken);
string user = api.GetEmailPlus();

using (Imap imap = new Imap())
{
    imap.ConnectSSL("imap.gmail.com");
    imap.LoginOAUTH2(user, accessToken);

    imap.SelectInbox();
    List<long> uids = imap.Search(Flag.Unseen);

    foreach (long uid in uids)
    {
        var eml = imap.GetMessageByUID(uid);
        IMail email = new MailBuilder().CreateFromEml(eml);
        Console.WriteLine(email.Subject);
    }
    imap.Close();
}

NativeApplicationClient class

The OAuth 2.0 client for use by native applications. It’s main purpose is to build a generic URL containing the auth code, because DotNetOpenAuth library only allows parsing an URL as a method of retrieving the AuthorizationState.

/// <summary>
/// The OAuth2 client for use by native applications. 
/// This is a partial implementation which  should be used until 
/// the feature has been fully implemented in DotNetOpenAuth.
/// </summary>
public class NativeApplicationClient : UserAgentClient
{
    /// <summary>
    /// Represents a callback URL which points to a special out of band page 
    /// used for native OAuth2 authorization. This URL will cause the authorization 
    /// code to appear in the title of the window.
    /// </summary>
    /// <remarks>
    /// See http://code.google.com/apis/accounts/docs/OAuth2.html
    /// </remarks>
    public const string OutOfBandCallbackUrl = "urn:ietf:wg:oauth:2.0:oob";

    /// <summary>
    /// Initializes a new instance of the <see cref="UserAgentClient"/> class.
    /// </summary>
    /// <param name="authorizationServer">The token issuer.</param>
    /// <param name="clientIdentifier">The client identifier.</param>
    /// <param name="clientSecret">The client secret.</param>
    public NativeApplicationClient(
        AuthorizationServerDescription authorizationServer,
        string clientIdentifier,
        string clientSecret)
        : base(authorizationServer, clientIdentifier, clientSecret)
    {
    }

    /// <summary>
    /// Initializes a new instance of the <see cref="UserAgentClient"/> class.
    /// </summary>
    /// <param name="authorizationServer">The token issuer.</param>
    public NativeApplicationClient(
        AuthorizationServerDescription authorizationServer)
        : this(authorizationServer, null, null)
    {
    }

    /// <summary>
    /// Creates the URL which should be used by the user to request the initial 
    /// authorization. Uses the default Out-of-band-URI as a callback.
    /// </summary>
    /// <param name="scope">Set of requested scopes</param>
    /// <returns>URI pointing to the authorization server</returns>
    public Uri RequestUserAuthorization(IEnumerable<string> scope)
    {
        var state = new AuthorizationState(scope);
        state.Callback = new Uri(OutOfBandCallbackUrl);
        return RequestUserAuthorization(state, false, null);
    }

    /// <summary>
    /// Uses the provided authorization code to create an authorization state.
    /// </summary>
    /// <param name="authCode">The authorization code for getting an access token.</param>
    /// <param name="authorizationState">The authorization.  Optional.</param>
    /// <returns>The granted authorization, or <c>null</c> if the authorization was null or rejected.</returns>
    public IAuthorizationState ProcessUserAuthorization(
        string authCode, 
        IAuthorizationState authorizationState)
    {
        if (authorizationState == null)
        {
            authorizationState = new AuthorizationState(null);
            authorizationState.Callback = new Uri(OutOfBandCallbackUrl);
        }

        // Build a generic URL containing the auth code.
        // This is done here as we cannot modify the DotNetOpenAuth library 
        // and the underlying method only allows parsing an URL as a method 
        // of retrieving the AuthorizationState.
        string url = "http://example.com/?code=" + authCode;
        return ProcessUserAuthorization(new Uri(url), authorizationState);
    }

    /// <summary>
    /// Uses the provided authorization code to create an authorization state.
    /// </summary>
    /// <param name="authCode">The authorization code for getting an access token.</param>
    /// <returns>The granted authorization, or <c>null</c> if the authorization was null or rejected.</returns>
    public IAuthorizationState ProcessUserAuthorization(string authCode)
    {
        return ProcessUserAuthorization(authCode, null);
    }
};

Refreshing access token

An access token is usually short lived and valid for a maximum of one hour. The main reason behind this is security and prevention of replay attacks. This means that for long-lived applications you need to refresh the access token.

Your refresh token will be sent only once – don’t loose it!

We recommend storing entire IAuthorizationState object received from NativeApplicationClient.ProcessUserAuthorization method call. This object contains both: refresh token and access token, along with its expiration time.

The process of refreshing access token is simple:

IAuthorizationState grantedAccess = ...
consumer.RefreshAuthorization(grantedAccess, TimeSpan.FromMinutes(20));

In the example above the access token will not be refreshed if its remaining lifetime exceeds 20 minutes.

Retrieving lost refresh token

When your application receives a refresh token, it is important to store that refresh token for future use. If your application loses the refresh token, it will have to re-prompt the user for consent before obtaining another refresh token.

You’ll need to add approval_prompt=force to your parameters:

 AuthorizationServerDescription authServer = new AuthorizationServerDescription
 {
     AuthorizationEndpoint = 
          new Uri("https://accounts.google.com/o/oauth2/auth?access_type=offline&approval_prompt=force"),
     ...
 };