Pascal (Lazarus/Delphi)

Get GMail OAuth2 Access Token for Desktop App

See more GMail REST API Examples

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.

Pascal (Lazarus/Delphi)

program ChilkatDemo;

// Demonstrates using the Chilkat Pascal wrapper via the C bridge DLL.
// Builds as a console application under Lazarus (FPC) or Delphi.

{$IFDEF FPC}
  {$MODE DELPHI}
{$ENDIF}
{$APPTYPE CONSOLE}

uses
  {$IFDEF UNIX}
  cthreads,
  {$ENDIF}
  SysUtils,
  CkDllLoader,
  Chilkat.OAuth2,
  Chilkat.StringBuilder;

// ---------------------------------------------------------------------------

procedure RunDemo;
var
  success: Boolean;
  oauth2: TOAuth2;
  url: string;
  numMsWaited: Integer;
  sbJson: TStringBuilder;

begin
  success := False;

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

  oauth2 := TOAuth2.Create;

  //  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.
  url := oauth2.StartAuth();
  if (oauth2.LastMethodSuccess = False) then
    begin
      WriteLn(oauth2.LastErrorText);
      Exit;
    end;

  //  Launch the system's default browser navigated to the URL.
  success := oauth2.LaunchBrowser(url);
  if (success = False) then
    begin
      WriteLn(oauth2.LastErrorText);
      Exit;
    end;

  //  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();
      WriteLn('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
      WriteLn('OAuth2 failed to complete.');
      WriteLn(oauth2.FailureInfo);
      Exit;
    end;

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

  if (oauth2.AuthFlowState <> 3) then
    begin
      WriteLn('Unexpected AuthFlowState:' + oauth2.AuthFlowState);
      Exit;
    end;

  //  Save the full JSON access token response to a file.
  sbJson := TStringBuilder.Create;
  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"
  //  	}
  //  
  WriteLn('OAuth2 authorization granted!');
  WriteLn('Access Token = ' + oauth2.AccessToken);


  oauth2.Free;
  sbJson.Free;

end;

// ---------------------------------------------------------------------------

begin

  try
    RunDemo;
  except
    on E: Exception do
      WriteLn('Unhandled exception: ', E.ClassName, ': ', E.Message);
  end;

  WriteLn;
  {$IFDEF MSWINDOWS}
  WriteLn('Press Enter to exit...');
  ReadLn;
  {$ENDIF}
end.