(C#) OAuth2 for a GMail using a JSON Service Account Key

Demonstrates how get an OAuth2 access token for GMail (Google Service Account) using a JSON private key.

After the access token is obtained, it may be used to send email. When the access token expires, a new access token needs to be obtained (using this same procedure).

Note: This is for OAuth2 using Google Service account keys.

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// This example requires the Chilkat API to have been previously unlocked.
// See Global Unlock Sample for sample code.

// First load the JSON key into a string.
Chilkat.FileAccess fac = new Chilkat.FileAccess();
string jsonKey = fac.ReadEntireTextFile("qa_data/googleApi/ChilkatTest-ab2ecd52ef98.json","utf-8");
if (fac.LastMethodSuccess != true) {
    Debug.WriteLine(fac.LastErrorText);
    return;
}

// A JSON private key should look like this:

// 	{
// 	  "type": "service_account",
// 	  "project_id": "chilkattest-1350",
// 	  "private_key_id": "fa2e36ee26986eab628b59868af8bec1d1c64c38",
// 	  "private_key": "-----BEGIN PRIVATE KEY-----\nMIIEvgIjFa...28N64N2n1E4FYzBZjSdy\n-----END PRIVATE KEY-----\n",
// 	  "client_email": "598922945226-00rb0ppfg0sndajo6bhvd4v17jtj2d3a@developer.gserviceaccount.com",
// 	  "client_id": "598922945226-00rb0ppfg0snd9jo7bhvd4v17jtj2d3a.apps.googleusercontent.com",
// 	  "auth_uri": "https://accounts.google.com/o/oauth2/auth",
// 	  "token_uri": "https://accounts.google.com/o/oauth2/token",
// 	  "auth_provider_x509_cert_url": "https://www.googleapis.com/oauth2/v1/certs",
// 	  "client_x509_cert_url": "https://www.googleapis.com/robot/v1/metadata/x509/598922945226-00rb0ppfg0sndajo6bhvd4v17jtj2d3a%40developer.gserviceaccount.com"
// 	}

Chilkat.AuthGoogle gAuth = new Chilkat.AuthGoogle();
gAuth.JsonKey = jsonKey;

// Choose a scope.
gAuth.Scope = "https://mail.google.com/";

// Request an access token that is valid for this many seconds.
gAuth.ExpireNumSeconds = 3600;

// If the application is requesting delegated access:
// The email address of the user for which the application is requesting delegated access,
// then set the email address here. (Otherwise leave it empty.)
gAuth.SubEmailAddress = "";

// Connect to www.googleapis.com using TLS (TLS 1.2 is the default.)
// The Chilkat socket object is used so that the connection can be established
// through proxies or an SSH tunnel if desired.
Chilkat.Socket tlsSock = new Chilkat.Socket();
bool success = tlsSock.Connect("www.googleapis.com",443,true,5000);
if (success != true) {
    Debug.WriteLine(tlsSock.LastErrorText);
    return;
}

// Send the request to obtain the access token.
success = gAuth.ObtainAccessToken(tlsSock);
if (success != true) {
    Debug.WriteLine(gAuth.LastErrorText);
    return;
}

// Examine the access token:
Debug.WriteLine("Access Token: " + gAuth.AccessToken);

// Now that we have the access token, it may be used to send email
// while it remains valid.  Once the access token expires, a new access token 
// should be obtained using the same code as above.

// -----------------------------------------------------------------------
Chilkat.MailMan mailman = new Chilkat.MailMan();

// Set the properties for the GMail SMTP server:
mailman.SmtpHost = "smtp.gmail.com";
mailman.SmtpPort = 587;
mailman.StartTLS = true;

mailman.SmtpUsername = "YOUR_GOOGLE_APPS_USER_EMAIL_ADDRESS";
mailman.OAuth2AccessToken = gAuth.AccessToken;

// Create a new email object
Chilkat.Email email = new Chilkat.Email();

email.Subject = "This is a test";
email.Body = "This is a test";
email.From = "YOUR NAME <YOUR_GOOGLE_APPS_USER_EMAIL_ADDRESS>";
success = email.AddTo("Chilkat Admin","admin@chilkatsoft.com");
// To add more recipients, call AddTo, AddCC, or AddBcc once per recipient.

// Call SendEmail to connect to the SMTP server and send.
// The connection (i.e. session) to the SMTP server remains
// open so that subsequent SendEmail calls may use the
// same connection.  
success = mailman.SendEmail(email);
if (success != true) {
    Debug.WriteLine(mailman.LastErrorText);
    return;
}

// You may close the connection here.  If the connection is kept open, 
// the next call to mailman.SendEmail will continue using the already-established connection
// (and automatically re-connect if needed).
success = mailman.CloseSmtpConnection();
if (success != true) {
    Debug.WriteLine("Connection to SMTP server not closed cleanly.");
}

Debug.WriteLine("Email Sent via GMail using an OAuth2 Service Account Key.");