(JavaScript) Get GMail OAuth2 Access Token for Desktop App

Demonstrates how to get a GMail OAuth2 access token from a desktop application or script.

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. To complete this example, you will need to find out how to display a web browser and navigate to the URL returned by the call to oauth2.StartAuth.

Note

This example is intended for running within a Chilkat.Js embedded JavaScript engine. All Chilkat JavaScript examples require Chilkat v11.4.0 or greater.

var success = false;

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

var oauth2 = new CkOAuth2();

// 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 = true;
oauth2.CodeChallengeMethod = "S256";

// See https://developers.google.com/gmail/api/auth/scopes for a list of GMail scopes.
// This is the full-permissions scope for GMail.
oauth2.Scope = "https://mail.google.com/";

// Important note about GMail scope for sending email:
// If the SMTP protocol is used for sending, then the full GMail scope is required: "https://mail.google.com/"
// Here is an example that sends GMail via the SMTP protocol:  Send GMail using SMTP
// If the GMail REST API is used, then the more restrictive Gmail scope can be used:  "https://www.googleapis.com/auth/gmail.send"
// Here is an example that sends GMail using the GMail REST API: Send GMail using REST API

// Begin the OAuth2 three-legged flow.  This returns a URL that should be loaded in a browser.
var url = oauth2.StartAuth();
if (oauth2.LastMethodSuccess == false) {
    console.log(oauth2.LastErrorText);
    return;
}

// Launch the system's default browser navigated to the URL.
success = oauth2.LaunchBrowser(url);
if (success == false) {
    console.log(oauth2.LastErrorText);
    return;
}

// Now wait for the authorization.
// We'll wait for a max of 30 seconds.
var numMsWaited = 0;
while ((numMsWaited < 30000) && (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();
    console.log("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.AuthFlowState == 5) {
    console.log("OAuth2 failed to complete.");
    console.log(oauth2.FailureInfo);
    return;
}

if (oauth2.AuthFlowState == 4) {
    console.log("OAuth2 authorization was denied.");
    console.log(oauth2.AccessTokenResponse);
    return;
}

if (oauth2.AuthFlowState !== 3) {
    console.log("Unexpected AuthFlowState:" + oauth2.AuthFlowState);
    return;
}

// Save the full JSON access token response to a file.
var sbJson = new CkStringBuilder();
sbJson.Append(oauth2.AccessTokenResponse);
sbJson.WriteFile("qa_data/tokens/gmail.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"
// 	}
// 
console.log("OAuth2 authorization granted!");
console.log("Access Token = " + oauth2.AccessToken);