(Delphi ActiveX) Facebook OAuth2 Access Token

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

Chilkat for Delphi Downloads Chilkat ActiveX DLL for Delphi Chilkat non-ActiveX DLL for Delphi * The examples here use the ActiveX DLL.

uses
    Winapi.Windows, Winapi.Messages, System.SysUtils, System.Variants, System.Classes, Vcl.Graphics,
    Vcl.Controls, Vcl.Forms, Vcl.Dialogs, Vcl.StdCtrls, Chilkat_TLB;

...

procedure TForm1.Button1Click(Sender: TObject);
var
oauth2: TChilkatOAuth2;
success: Integer;
url: WideString;
numMsWaited: Integer;

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

oauth2 := TChilkatOAuth2.Create(Self);

// This should match the Site URL configured for your Facebook APP, such as "http://localhost:3017/"
oauth2.ListenPort := 3017;

oauth2.AuthorizationEndpoint := 'https://www.facebook.com/dialog/oauth';
oauth2.TokenEndpoint := 'https://graph.facebook.com/oauth/access_token';

// Replace these with actual values.
oauth2.ClientId := 'FACEBOOK-CLIENT-ID';
oauth2.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.
oauth2.Scope := 'public_profile,user_friends,email,user_posts,user_likes,user_photos,publish_actions';

oauth2.CodeChallenge := 1;
oauth2.CodeChallengeMethod := 'S256';

// Begin the OAuth2 three-legged flow.  This returns a URL that should be loaded in a browser.
url := oauth2.StartAuth();
if (oauth2.LastMethodSuccess <> 1) then
  begin
    Memo1.Lines.Add(oauth2.LastErrorText);
    Exit;
  end;

// 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.
numMsWaited := 0;
while (numMsWaited < 30000) and (oauth2.AuthFlowState < 3) do
  begin
    oauth2.SleepMs(100);
    numMsWaited := numMsWaited + 100;
  end;

// 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) then
  begin
    oauth2.Cancel();
    Memo1.Lines.Add('No response from the browser!');
    Exit;
  end;

// 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) then
  begin
    Memo1.Lines.Add('OAuth2 failed to complete.');
    Memo1.Lines.Add(oauth2.FailureInfo);
    Exit;
  end;

if (oauth2.AuthFlowState = 4) then
  begin
    Memo1.Lines.Add('OAuth2 authorization was denied.');
    Memo1.Lines.Add(oauth2.AccessTokenResponse);
    Exit;
  end;

if (oauth2.AuthFlowState <> 3) then
  begin
    Memo1.Lines.Add('Unexpected AuthFlowState:' + IntToStr(oauth2.AuthFlowState));
    Exit;
  end;

Memo1.Lines.Add('OAuth2 authorization granted!');
Memo1.Lines.Add('Access Token = ' + oauth2.AccessToken);
end;