(Java) 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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import com.chilkatsoft.*;

public class ChilkatExample {

  static {
    try {
        System.loadLibrary("chilkat");
    } catch (UnsatisfiedLinkError e) {
      System.err.println("Native code library failed to load.\n" + e);
      System.exit(1);
    }
  }

  public static void main(String argv[])
  {
    // 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.
    CkFileAccess fac = new CkFileAccess();
    String jsonKey = fac.readEntireTextFile("qa_data/googleApi/ChilkatTest-ab2ecd52ef98.json","utf-8");
    if (fac.get_LastMethodSuccess() != true) {
        System.out.println(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"
    // 	}

    CkAuthGoogle gAuth = new CkAuthGoogle();
    gAuth.put_JsonKey(jsonKey);

    // Choose a scope.
    gAuth.put_Scope("https://mail.google.com/");

    // Request an access token that is valid for this many seconds.
    gAuth.put_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.put_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.
    CkSocket tlsSock = new CkSocket();
    boolean success = tlsSock.Connect("www.googleapis.com",443,true,5000);
    if (success != true) {
        System.out.println(tlsSock.lastErrorText());
        return;
        }

    // Send the request to obtain the access token.
    success = gAuth.ObtainAccessToken(tlsSock);
    if (success != true) {
        System.out.println(gAuth.lastErrorText());
        return;
        }

    // Examine the access token:
    System.out.println("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.

    // -----------------------------------------------------------------------
    CkMailMan mailman = new CkMailMan();

    // Set the properties for the GMail SMTP server:
    mailman.put_SmtpHost("smtp.gmail.com");
    mailman.put_SmtpPort(587);
    mailman.put_StartTLS(true);

    mailman.put_SmtpUsername("YOUR_GOOGLE_APPS_USER_EMAIL_ADDRESS");
    mailman.put_OAuth2AccessToken(gAuth.accessToken());

    // Create a new email object
    CkEmail email = new CkEmail();

    email.put_Subject("This is a test");
    email.put_Body("This is a test");
    email.put_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) {
        System.out.println(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) {
        System.out.println("Connection to SMTP server not closed cleanly.");
        }

    System.out.println("Email Sent via GMail using an OAuth2 Service Account Key.");
  }
}