(Lianja) 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.

Chilkat Lianja Extension Download Chilkat Lianja Extension

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

loOauth2 = createobject("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.
loOauth2.ListenPort = 55568

loOauth2.AuthorizationEndpoint = "https://accounts.google.com/o/oauth2/v2/auth"
loOauth2.TokenEndpoint = "https://www.googleapis.com/oauth2/v4/token"

// Replace these with actual values.
loOauth2.ClientId = "GOOGLE-CLIENT-ID"
loOauth2.ClientSecret = "GOOGLE-CLIENT-SECRET"

loOauth2.CodeChallenge = .T.
loOauth2.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.
loOauth2.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.
lcUrl = loOauth2.StartAuth()
if (loOauth2.LastMethodSuccess <> .T.) then
    ? loOauth2.LastErrorText
    release loOauth2
    return
endif

// 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 QuickBooks 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.
lnNumMsWaited = 0
do while (lnNumMsWaited < 30000) and (loOauth2.AuthFlowState < 3)
    loOauth2.SleepMs(100)
    lnNumMsWaited = lnNumMsWaited + 100
enddo

// 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 (loOauth2.AuthFlowState < 3) then
    loOauth2.Cancel()
    ? "No response from the browser!"
    release loOauth2
    return
endif

// 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 (loOauth2.AuthFlowState = 5) then
    ? "OAuth2 failed to complete."
    ? loOauth2.FailureInfo
    release loOauth2
    return
endif

if (loOauth2.AuthFlowState = 4) then
    ? "OAuth2 authorization was denied."
    ? loOauth2.AccessTokenResponse
    release loOauth2
    return
endif

if (loOauth2.AuthFlowState <> 3) then
    ? "Unexpected AuthFlowState:" + str(loOauth2.AuthFlowState)
    release loOauth2
    return
endif

// Save the full JSON access token response to a file.
loSbJson = createobject("CkStringBuilder")
loSbJson.Append(loOauth2.AccessTokenResponse)
loSbJson.WriteFile("qa_data/tokens/gmail.json","utf-8",.F.)

// 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"
// 	}
// 
? "OAuth2 authorization granted!"
? "Access Token = " + loOauth2.AccessToken


release loOauth2
release loSbJson