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

In this post I’ll show how to access Gmail account using 3-legged OAuth authentication method. The key advantage of this method is that it allows an application to access user email without knowing user’s password.

You can read more on OAuth authentication with Google accounts here:
http://code.google.com/apis/accounts/docs/OAuth_ref.html

Gmail IMAP and SMTP using OAuth:
http://code.google.com/apis/gmail/oauth/protocol.html

If your application/website is not registered, you should use following key and secret:
consumer key: “anonymous”
consumer secret: “anonymous”

Remember to add reference to Maill.dll and appropriate namespaces.

// C#

using Lesnikowski.Client.IMAP;
using Lesnikowski.Client.Authentication;
using Lesnikowski.Client.Authentication.Google;

const string userEmailAccount = "pat@gmail.com";
const string consumerKey = "anonymous";
const string consumerSecret = "anonymous";

GmailOAuth oauth = new GmailOAuth(
    consumerKey, consumerSecret);

string url = oauth.GetAuthorizationUrl("http://localhost:64119/");

Process.Start(url);
// You can use Response.Redirect(url) in ASP.NET

string oauthVerifier = HttpUtility.UrlDecode(Console.ReadLine());
// You can use Request["oauth_verifier"].ToString() in ASP.NET

oauth.GetAccessToken(oauthVerifier);

using (Imap client = new Imap())
{
    client.ConnectSSL("imap.gmail.com");
    string oauthImapKey = oauth.GetXOAuthKeyForImap();
    client.LoginOAUTH(oauthImapKey);

    // Now you can access user's emails
    //...

    client.Close();
    oauth.RevokeToken(oauthImapKey);
}

1.
GmailOAuth.GetAuthorizationUrl method returns url you should redirect your user to so he can authorize access.
As you can see Mail.dll is asking for access to user’s email information and Gmail access:

2.
If you don’t specify callback parameter, user will have to manually copy&paste the token to your application:

In case of a web project, you can specify a web address on your website. oauth_verifier will be included as the redirection url parameter.

After the redirection, your website/application needs to read oauth_verifier query parameter:

3.
GmailOAuth.GetAccessToken method authorizes the token.

4.
GmailOAuth.GetXOAuthKeyForImap method uses Google API to get the email address of the user, and generates XOAuth key for IMAP protocol (you can use GetXOAuthKeyForSmtp for SMTP).

5.
GmailOAuth.RevokeToken method revokes XOAuth key, so no further access can be made with it.

…and finally VB.NET version of the code:

' VB.NET

Imports Lesnikowski.Client.IMAP
Imports Lesnikowski.Client.Authentication
Imports Lesnikowski.Client.Authentication.Google

Const userEmailAccount As String = "pat@gmail.com"
Const consumerKey As String = "anonymous"
Const consumerSecret As String = "anonymous"

Dim oauth As New GmailOAuth(consumerKey, consumerSecret)

Dim url As String = oauth.GetAuthorizationUrl("http://localhost:64119/")

Process.Start(url)
' You can use Response.Redirect(url) in ASP.NET

Dim oauthVerifier As String = HttpUtility.UrlDecode(Console.ReadLine())
' You can use Request["oauth_verifier"].ToString() in ASP.NET

oauth.GetAccessToken(oauthVerifier)

Using client As New Imap()
	client.ConnectSSL("imap.gmail.com")
	Dim oauthImapKey As String = oauth.GetXOAuthKeyForImap()
	client.LoginOAUTH(oauthImapKey)

	' Now you can access user's emails
	'...

	client.Close()
	oauth.RevokeToken(oauthImapKey)
End Using

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

In this post I’ll show how to access Gmail account using 2-legged OAuth authentication method. The basic idea is that domain administrator can use this method to access user email without knowing user’s password.

You can read more on OAuth authentication with Google accounts here:
http://code.google.com/apis/accounts/docs/OAuth_ref.html

Gmail IMAP and SMTP using OAuth:
http://code.google.com/apis/gmail/oauth/protocol.html

Remember to add reference to Maill.dll and appropriate namespaces.

// C#

using Lesnikowski.Client.IMAP;
using Lesnikowski.Client.Authentication;
using Lesnikowski.Client.Authentication.Google;

const string consumerKey = "example.com";
const string consumerSecret = "secret";
const string email = "pat@example.com";

Gmail2LeggedOAuth oauth = new Gmail2LeggedOAuth(
    consumerKey, consumerSecret);

using (Imap client = new Imap())
{
    client.ConnectSSL(TestConstants.GmailImapServer);

    string oauthImapKey = oauth.GetXOAuthKeyForImap(email);

    client.LoginOAUTH(oauthImapKey);

    //...

    client.Close();
}

' VB.NET

Imports Lesnikowski.Client.IMAP
Imports Lesnikowski.Client.Authentication
Imports Lesnikowski.Client.Authentication.Google

Const  consumerKey As String = "example.com"
Const  consumerSecret As String = "secret"
Const  email As String = "pat@example.com"

Dim oauth As New Gmail2LeggedOAuth(consumerKey, consumerSecret)

Using client As New Imap()
	client.ConnectSSL(TestConstants.GmailImapServer)

	Dim oauthImapKey As String = oauth.GetXOAuthKeyForImap(email)

	client.LoginOAUTH(oauthImapKey)

	'...

	client.Close()
End Using

Here are the google apps configuration screens:

This article describes generic OAuth class, if you are using Gmail please read 2-legged OAuth authentication with Gmail

Remember to add reference to Maill.dll and appropriate namespaces.

// C#

using Lesnikowski.Client.Authentication;
using Lesnikowski.Client.IMAP;

string consumerKey = "your_domain.com";
string consumerSecret = "your_oauth_consumer_secret";
string emailAccount = "address@your_domain.com";

using (Imap client = new Imap())
{
    client.ConnectSSL("imap.gmail.com");

    string imapUrl = string.Format(
        "https://mail.google.com/mail/b/{0}/imap/?xoauth_requestor_id={1}",
        emailAccount,
        HttpUtility.UrlEncode(emailAccount));

    string oauthImapKey = OAuth.ForUrl(imapUrl)
        .Consumer(consumerKey, consumerSecret)
        .SignatureMethod(SignatureType.HMACSHA1)
        .Sign()
        .GetXOAuthKey();

    client.LoginOAUTH(oauthImapKey);

    //...

    client.Close();
}

' VB.NET

Imports Lesnikowski.Client.Authentication
Imports Lesnikowski.Client.IMAP

Dim consumerKey As String = "example.com"
Dim consumerSecret As String = "secret"
Dim emailAccount As String = "pat@example.com"

Using client As New Imap()
    client.ConnectSSL("imap.gmail.com")

    Dim imapUrl As String = String.Format( _
        "https://mail.google.com/mail/b/{0}/imap/?xoauth_requestor_id={1}", _
        emailAccount, _
        HttpUtility.UrlEncode(emailAccount))

    Dim oauthImapKey As String = OAuth.ForUrl(imapUrl) _
        .Consumer(consumerKey, consumerSecret) _
        .SignatureMethod(SignatureType.HMACSHA1) _
        .Sign() _
        .GetXOAuthKey()

    client.LoginOAUTH(oauthImapKey)

    '...

    client.Close()
End Using

This article describes generic OAuth class, if you are using Gmail please read OAuth authentication with Gmail

The following code makes several HTTP requests to authenticate your application. It also fires up the web browser, so the user can allow or deny the application to access his emails.

Remember to add reference to Maill.dll and appropriate namespaces.

1.

// C#

using Lesnikowski.Client.Authentication;
using Lesnikowski.Client.IMAP;

const string userEmailAccount = "pat@gmail.com";
const string consumerKey = "anonymous";
const string consumerSecret = "anonymous";

// Get request token
ParameterList parameters1 = OAuth.ForUrl(
        "https://www.google.com/accounts/OAuthGetRequestToken")
    .Consumer(consumerKey, consumerSecret)
    .AddParameter("scope", "https://mail.google.com/")
   .AddParameter(OAuthParameterName.OAuthCallback, "oob")
    .Sign()
    .ExecuteWebRequest();

// Authorize token
string url2 = OAuth.ForUrl(
        "https://www.google.com/accounts/OAuthAuthorizeToken")
   .Consumer(consumerKey, consumerSecret)
   .Token(parameters1.GetValue(OAuthParameterName.OAuthToken))
   .TokenSecret(parameters1.GetValue(OAuthParameterName.OAuthTokenSecret))
   .Sign()
   .GetUrl();

// Fire up the browser.
Process.Start(url2);
// You can use Response.Redirect(url) in ASP.NET

2.
The user needs now to log-in to Gmail account (note that user does not enter credentials in your application):

3.
Then he needs to allow your application to access Gmail:

4.
If you don’t specify callback parameter, user will have to manually copy&paste the token to your application:

In case of a web project, instead of oob value as OAuthCallback parameter, you can specify a web address on your website. oauth_verifier will be included as the redirection url parameter.

After the redirection, your website/application needs to read oauth_verifier query parameter:

5.

// C#

Console.WriteLine("Please enter the key: ");
string oauth_verifier = Console.ReadLine();
// You can use Request["oauth_verifier"].ToString() in ASP.NET

// Get access token
ParameterList parameters3 = OAuth.ForUrl(
        "https://www.google.com/accounts/OAuthGetAccessToken")
   .Consumer(consumerKey, consumerSecret)
   .Token(parameters1.GetValue(OAuthParameterName.OAuthToken))
   .TokenSecret(parameters1.GetValue(OAuthParameterName.OAuthTokenSecret))
   .AddParameter("oauth_verifier", oauth_verifier)
   .Sign()
   .ExecuteWebRequest();

// Log-in to IMAP server using XOAuth
using (Imap client = new Imap())
{
    client.ConnectSSL(TestConstants.GmailImapServer);

    string imapUrl = string.Format(
        "https://mail.google.com/mail/b/{0}/imap/", userEmailAccount);

    string oauthImapKey = OAuth.ForUrl(imapUrl)
        .Consumer(consumerKey, consumerSecret)
        .Token(parameters3.GetValue(OAuthParameterName.OAuthToken))
        .TokenSecret(parameters3.GetValue(OAuthParameterName.OAuthTokenSecret))
        .Sign()
        .GetXOAuthKey();

    client.LoginOAUTH(oauthImapKey);

    // Now you can access user's emails.
    //...

    client.Close();
}

Here’s the VB.NET version of the code samples:

Remember to add reference to Maill.dll and appropriate namespaces.

1.

' VB.NET

import Lesnikowski.Client.Authentication
import Lesnikowski.Client.IMAP

Const  userEmailAccount As String = "alice@gmail.com"
Const  consumerKey As String = "anonymous"
Const  consumerSecret As String = "anonymous"

' Gget request token
Dim parameters1 As ParameterList = OAuth _
	.ForUrl("https://www.google.com/accounts/OAuthGetRequestToken") _
	.Consumer(consumerKey, consumerSecret) _
	.AddParameter("scope", "https://mail.google.com/") _
	.AddParameter(OAuthParameterName.OAuthCallback, "oob") _
	.Sign() _
	.ExecuteWebRequest()

' Authorize token
Dim url2 As String = OAuth _
	.ForUrl("https://www.google.com/accounts/OAuthAuthorizeToken") _
	.Consumer(consumerKey, consumerSecret) _
	.Token(parameters1.GetValue(OAuthParameterName.OAuthToken)) _
	.TokenSecret(parameters1.GetValue(OAuthParameterName.OAuthTokenSecret)) _
	.Sign() _
	.GetUrl()

' Fire up the browser
Process.Start(url2)
' You can use Response.Redirect(url) in ASP.NET

2.
First the user needs to log in to Gmail account (note that user does not enter credentials in your application):

3.
Then he needs to allow your application to access Gmail:

4.
If you don’t specify callback parameter, user will have to manually copy&paste the token to your application:

In case of a web project, instead of oob value as OAuthCallback parameter, you can specify a web address on your website. oauth_verifier will be included as the redirection url parameter.

After the redirection, your website/application needs to read oauth_verifier query parameter:

5.

' VB.NET

Console.WriteLine("Please enter the key: ")
Dim oauth_verifier As String = Console.ReadLine().Trim()
' You can use Request("oauth_verifier").ToString() in ASP.NET

' Third: get access token
Dim parameters3 As ParameterList = OAuth _
	.ForUrl("https://www.google.com/accounts/OAuthGetAccessToken") _
	.Consumer(consumerKey, consumerSecret) _
	.Token(parameters1.GetValue(OAuthParameterName.OAuthToken)) _
	.TokenSecret(parameters1.GetValue(OAuthParameterName.OAuthTokenSecret)) _
	.AddParameter("oauth_verifier", oauth_verifier) _
	.Sign() _
	.ExecuteWebRequest()

' Log-in to IMAP server using XOAuth
Using client As New Imap()
	client.ConnectSSL(TestConstants.GmailImapServer)

	Dim imapUrl As String = String.Format("https://mail.google.com/mail/b/{0}/imap/", userEmailAccount)

	Dim oauthImapKey As String = OAuth.ForUrl(imapUrl) _
		.Consumer(consumerKey, consumerSecret) _
		.Token(parameters3.GetValue(OAuthParameterName.OAuthToken)) _
		.TokenSecret(parameters3.GetValue(OAuthParameterName.OAuthTokenSecret)) _
		.Sign() _
		.GetXOAuthKey()

	client.LoginOAUTH(oauthImapKey)

	' Now you can access user's emails.
        ' ...

	client.Close()
End Using