(Visual FoxPro) Facebook OAuth2 Access Token

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

Chilkat ActiveX Downloads ActiveX for 32-bit and 64-bit Windows

LOCAL loOauth2
LOCAL lnSuccess
LOCAL lcUrl
LOCAL lnNumMsWaited

* It requires the Chilkat API to have been previously unlocked.
* See Global Unlock Sample for sample code.

* For versions of Chilkat < 10.0.0, use CreateObject('Chilkat_9_5_0.OAuth2')
loOauth2 = CreateObject('Chilkat.OAuth2')

* This should match the Site URL configured for your Facebook APP, such as "http://localhost:3017/"
loOauth2.ListenPort = 3017

loOauth2.AuthorizationEndpoint = "https://www.facebook.com/dialog/oauth"
loOauth2.TokenEndpoint = "https://graph.facebook.com/oauth/access_token"

* Replace these with actual values.
loOauth2.ClientId = "FACEBOOK-CLIENT-ID"
loOauth2.ClientSecret = "FACEBOOK-CLIENT-SECRET"

* Set the Scope to a comma-separated list of permissions the app wishes to request.
* See https://developers.facebook.com/docs/facebook-login/permissions/ for a full list of permissions.
loOauth2.Scope = "public_profile,user_friends,email,user_posts,user_likes,user_photos,publish_actions"

loOauth2.CodeChallenge = 1
loOauth2.CodeChallengeMethod = "S256"

* Begin the OAuth2 three-legged flow.  This returns a URL that should be loaded in a browser.
lcUrl = loOauth2.StartAuth()
IF (loOauth2.LastMethodSuccess <> 1) THEN
    ? loOauth2.LastErrorText
    RELEASE loOauth2
    CANCEL
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 Facebook 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
    CANCEL
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
    CANCEL
ENDIF

IF (loOauth2.AuthFlowState = 4) THEN
    ? "OAuth2 authorization was denied."
    ? loOauth2.AccessTokenResponse
    RELEASE loOauth2
    CANCEL
ENDIF

IF (loOauth2.AuthFlowState <> 3) THEN
    ? "Unexpected AuthFlowState:" + STR(loOauth2.AuthFlowState)
    RELEASE loOauth2
    CANCEL
ENDIF

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

RELEASE loOauth2