Xbase++

Get POP3 GMail OAuth2 Access Token for Desktop App

See more GMail SMTP/IMAP/POP Examples

Demonstrates how to get a POP3 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.

Xbase++

LOCAL nSuccess
LOCAL oOauth2
LOCAL cUrl
LOCAL nNumMsWaited
LOCAL oSbJson

nSuccess := 0

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

oOauth2 := CreateObject("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.
oOauth2:ListenPort := 55568

oOauth2:AuthorizationEndpoint := "https://accounts.google.com/o/oauth2/v2/auth"
oOauth2:TokenEndpoint := "https://www.googleapis.com/oauth2/v4/token"

//  Replace these with actual values.
oOauth2:ClientId := "GOOGLE-CLIENT-ID"
oOauth2:ClientSecret := "GOOGLE-CLIENT-SECRET"

oOauth2:CodeChallenge := 1
oOauth2: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, which is sufficient for all POP3 operations to pop.gmail.com
oOauth2: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.
cUrl := oOauth2:StartAuth()
IF (oOauth2:LastMethodSuccess == 0)
    ? oOauth2:LastErrorText
    oOauth2:destroy()
    RETURN
ENDIF

//  Launch the system's default browser navigated to the URL.
nSuccess := oOauth2:LaunchBrowser(cUrl)
IF (nSuccess == 0)
    ? oOauth2:LastErrorText
    oOauth2:destroy()
    RETURN
ENDIF

//  Now wait for the authorization.
//  We'll wait for a max of 30 seconds.
nNumMsWaited := 0
DO WHILE (nNumMsWaited < 30000) .AND. (oOauth2:AuthFlowState < 3)
    oOauth2:SleepMs(100)
    nNumMsWaited := nNumMsWaited + 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 (oOauth2:AuthFlowState < 3)
    oOauth2:Cancel()
    ? "No response from the browser!"
    oOauth2:destroy()
    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 (oOauth2:AuthFlowState == 5)
    ? "OAuth2 failed to complete."
    ? oOauth2:FailureInfo
    oOauth2:destroy()
    RETURN
ENDIF

IF (oOauth2:AuthFlowState == 4)
    ? "OAuth2 authorization was denied."
    ? oOauth2:AccessTokenResponse
    oOauth2:destroy()
    RETURN
ENDIF

IF (oOauth2:AuthFlowState != 3)
    ? "Unexpected AuthFlowState:" + Str(oOauth2:AuthFlowState)
    oOauth2:destroy()
    RETURN
ENDIF

//  Save the full JSON access token response to a file.
oSbJson := CreateObject("Chilkat.StringBuilder")
oSbJson:Append(oOauth2:AccessTokenResponse)
oSbJson:WriteFile("qa_data/tokens/gmail_pop3.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"
//  	}
//  
? "OAuth2 authorization granted!"
? "Access Token = " + oOauth2:AccessToken

oOauth2:destroy()
oSbJson:destroy()