(Android™) Get GMail SMTP OAuth2 Access Token for Desktop App

Demonstrates how to get a GMail SMTP OAuth2 access token from a desktop application or script, which can be used with the XOAUTH2 authentication method.

This example requires a browser window to be displayed to allow the GMail account owner to authorize the access. The code for displaying the web browser is omitted. Suggestions for a few programming languages are provided in code comments. You'll need to find out how to display a web browser and navigate to the URL returned by the call to oauth2.StartAuth.

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// Important: Don't forget to include the call to System.loadLibrary
// as shown at the bottom of this code sample.
package com.test;

import android.app.Activity;
import com.chilkatsoft.*;

import android.widget.TextView;
import android.os.Bundle;

public class SimpleActivity extends Activity {

  private static final String TAG = "Chilkat";

  // Called when the activity is first created.
  @Override
  public void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);

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

    CkOAuth2 oauth2 = new CkOAuth2();
    boolean success;

    // For Google OAuth2, set the listen port equal to the port used
    // in the Authorized Redirect URL for the Client ID.
    // For example, in this case the Authorized Redirect URL would be http://localhost:55568/
    // Your app should choose a port not likely not used by any other application.
    oauth2.put_ListenPort(55568);

    oauth2.put_AuthorizationEndpoint("https://accounts.google.com/o/oauth2/v2/auth");
    oauth2.put_TokenEndpoint("https://www.googleapis.com/oauth2/v4/token");

    // Replace these with actual values.
    oauth2.put_ClientId("GOOGLE-CLIENT-ID");
    oauth2.put_ClientSecret("GOOGLE-CLIENT-SECRET");

    oauth2.put_CodeChallenge(true);
    oauth2.put_CodeChallengeMethod("S256");

    // This is the full-permissions scope for GMail.
    oauth2.put_Scope("https://mail.google.com/");

    // -------------------------------------------------------------------------------------------------------
    // Important: Google claims there is a send-only scope:  "https://www.googleapis.com/auth/gmail.send"
    // However, it has been found to NOT work when sending email using the SMTP protocol.
    // Perhaps it works for sending GMail using the GMail REST API, but it most certainly does not
    // provide access/authentication for sending email by SMTP.  The full GMail scope is required.
    // In any case, it may be much easier to avoid using OAuth2 altogether and instead use "App Passwords".
    // See Send GMail with App Passwords.
    // -------------------------------------------------------------------------------------------------------

    // Begin the OAuth2 three-legged flow.  This returns a URL that should be loaded in a browser.
    String url = oauth2.startAuth();
    if (oauth2.get_LastMethodSuccess() != true) {
        Log.i(TAG, oauth2.lastErrorText());
        return;
        }

    // At this point, your application should load the URL in a browser.
    // For example, 
    // in C#: System.Diagnostics.Process.Start(url);
    //  in Java: Desktop.getDesktop().browse(new URI(url));
    //  in VBScript: Set wsh=WScript.CreateObject("WScript.Shell")
    //              wsh.Run url
    // in Xojo: ShowURL(url)  (see http://docs.xojo.com/index.php/ShowURL)
    // in Dataflex: Runprogram Background "c:\Program Files\Internet Explorer\iexplore.exe" sUrl        
    // The Google account owner would interactively accept or deny the authorization request.

    // Add the code to load the url in a web browser here...
    // Add the code to load the url in a web browser here...
    // Add the code to load the url in a web browser here...

    // Now wait for the authorization.
    // We'll wait for a max of 30 seconds.
    int numMsWaited = 0;
    while ((numMsWaited < 30000) and (oauth2.get_AuthFlowState() < 3)) {
        oauth2.SleepMs(100);
        numMsWaited = numMsWaited + 100;
        }

    // If there was no response from the browser within 30 seconds, then 
    // the AuthFlowState will be equal to 1 or 2.
    // 1: Waiting for Redirect. The OAuth2 background thread is waiting to receive the redirect HTTP request from the browser.
    // 2: Waiting for Final Response. The OAuth2 background thread is waiting for the final access token response.
    // In that case, cancel the background task started in the call to StartAuth.
    if (oauth2.get_AuthFlowState() < 3) {
        oauth2.Cancel();
        Log.i(TAG, "No response from the browser!");
        return;
        }

    // Check the AuthFlowState to see if authorization was granted, denied, or if some error occurred
    // The possible AuthFlowState values are:
    // 3: Completed with Success. The OAuth2 flow has completed, the background thread exited, and the successful JSON response is available in AccessTokenResponse property.
    // 4: Completed with Access Denied. The OAuth2 flow has completed, the background thread exited, and the error JSON is available in AccessTokenResponse property.
    // 5: Failed Prior to Completion. The OAuth2 flow failed to complete, the background thread exited, and the error information is available in the FailureInfo property.
    if (oauth2.get_AuthFlowState() == 5) {
        Log.i(TAG, "OAuth2 failed to complete.");
        Log.i(TAG, oauth2.failureInfo());
        return;
        }

    if (oauth2.get_AuthFlowState() == 4) {
        Log.i(TAG, "OAuth2 authorization was denied.");
        Log.i(TAG, oauth2.accessTokenResponse());
        return;
        }

    if (oauth2.get_AuthFlowState() != 3) {
        Log.i(TAG, "Unexpected AuthFlowState:" + String.valueOf(oauth2.get_AuthFlowState()));
        return;
        }

    // Save the full JSON access token response to a file.
    CkStringBuilder sbJson = new CkStringBuilder();
    sbJson.Append(oauth2.accessTokenResponse());
    sbJson.WriteFile("qa_data/tokens/_gmailSmtp.json","utf-8",false);

    // The saved JSON response looks like this:

    // 	{
    // 	 "access_token": "ya39.Ci-XA_C5bGgRDC3UaD-h0_NeL-DVIQnI2gHtBBBHkZzrwlARkwX6R3O0PCDEzRlfaQ",
    // 	 "token_type": "Bearer",
    // 	 "expires_in": 3600,
    // 	 "refresh_token": "1/r_2c_7jddspcdfesrrfKqfXtqo08D6Q-gUU0DsdfVMsx0c"
    // 	}
    // 
    Log.i(TAG, "OAuth2 authorization granted!");
    Log.i(TAG, "Access Token = " + oauth2.accessToken());

  }

  static {
      System.loadLibrary("chilkat");

      // Note: If the incorrect library name is passed to System.loadLibrary,
      // then you will see the following error message at application startup:
      //"The application <your-application-name> has stopped unexpectedly. Please try again."
  }
}