(PHP ActiveX) 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.

Chilkat ActiveX Downloads ActiveX for 32-bit and 64-bit Windows Note: The php_com_dotnet.dll may need to be enabled inside of php.ini.

<?php

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

// For versions of Chilkat < 10.0.0, use new COM('Chilkat_9_5_0.Chilkat.OAuth2')
$oauth2 = new COM("Chilkat.OAuth2");

// 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->ListenPort = 55568;

$oauth2->AuthorizationEndpoint = 'https://accounts.google.com/o/oauth2/v2/auth';
$oauth2->TokenEndpoint = 'https://www.googleapis.com/oauth2/v4/token';

// Replace these with actual values.
$oauth2->ClientId = 'GOOGLE-CLIENT-ID';
$oauth2->ClientSecret = 'GOOGLE-CLIENT-SECRET';

$oauth2->CodeChallenge = 1;
$oauth2->CodeChallengeMethod = 'S256';

// This is the full-permissions scope for GMail.
// oauth2.Scope = "https://mail.google.com/";
$oauth2->Scope = 'https://www.googleapis.com/auth/gmail.send';

// -------------------------------------------------------------------------------------------------------
// 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.
$url = $oauth2->startAuth();
if ($oauth2->LastMethodSuccess != 1) {
    print $oauth2->LastErrorText . "\n";
    exit;
}

// 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 60 seconds.
$numMsWaited = 0;
while (($numMsWaited < 60000) and ($oauth2->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->AuthFlowState < 3) {
    $oauth2->Cancel();
    print 'No response from the browser!' . "\n";
    exit;
}

// 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->AuthFlowState == 5) {
    print 'OAuth2 failed to complete.' . "\n";
    print $oauth2->FailureInfo . "\n";
    exit;
}

if ($oauth2->AuthFlowState == 4) {
    print 'OAuth2 authorization was denied.' . "\n";
    print $oauth2->AccessTokenResponse . "\n";
    exit;
}

if ($oauth2->AuthFlowState != 3) {
    print 'Unexpected AuthFlowState:' . $oauth2->AuthFlowState . "\n";
    exit;
}

// Save the full JSON access token response to a file.
// For versions of Chilkat < 10.0.0, use new COM('Chilkat_9_5_0.Chilkat.StringBuilder')
$sbJson = new COM("Chilkat.StringBuilder");
$sbJson->Append($oauth2->AccessTokenResponse);
$sbJson->WriteFile('qa_data/tokens/_gmailSmtp.json','utf-8',0);

// 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"
// 	}
// 
print 'OAuth2 authorization granted!' . "\n";
print 'Access Token = ' . $oauth2->AccessToken . "\n";

?>