(Delphi ActiveX) Get Google API Access Token using JSON Private Key

Demonstrates how to get a Google API access token using a JSON service account private key.

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
fac: TCkFileAccess;
jsonKey: WideString;
gAuth: TChilkatAuthGoogle;
tlsSock: TChilkatSocket;
success: Integer;
accessToken: WideString;
mailman: TChilkatMailMan;
email: TChilkatEmail;

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

// --------------------------------------------------------------------------------
// For a step-by-step guide for setting up your Google Workspace service account,
// see Setup Google Workspace Account for Sending SMTP GMail from a Service Account
// --------------------------------------------------------------------------------

// First load the JSON key into a string.
fac := TCkFileAccess.Create(Self);
jsonKey := fac.ReadEntireTextFile('qa_data/googleApi/chilkat25-b4214220e565.json','utf-8');
if (fac.LastMethodSuccess <> 1) then
  begin
    Memo1.Lines.Add(fac.LastErrorText);
    Exit;
  end;

// A Google service account JSON private key looks like this:

// {
//   "type": "service_account",
//   "project_id": "chilkat25",
//   "private_key_id": "b4214220f565881e19eeb97c2699bf5a0d1e3e0b",
//   "private_key": "-----BEGIN PRIVATE KEY-----\nMIIEvQ...NXcM=\n-----END PRIVATE KEY-----\n",
//   "client_email": "chilkatsvc@chilkat25.iam.gserviceaccount.com",
//   "client_id": "109122032928932715958",
//   "auth_uri": "https://accounts.google.com/o/oauth2/auth",
//   "token_uri": "https://oauth2.googleapis.com/token",
//   "auth_provider_x509_cert_url": "https://www.googleapis.com/oauth2/v1/certs",
//   "client_x509_cert_url": "https://www.googleapis.com/robot/v1/metadata/x509/chilkatsvc%40chilkat25.iam.gserviceaccount.com",
//   "universe_domain": "googleapis.com"
// }

gAuth := TChilkatAuthGoogle.Create(Self);
gAuth.JsonKey := jsonKey;

// Specify a scope.
gAuth.Scope := 'https://mail.google.com/';

// Request an access token that is valid for this many seconds.
gAuth.ExpireNumSeconds := 3600;

// When using a Google Workspace account with Gmail APIs, a service account can impersonate a user 
// via a process called domain-wide delegation — and the "sub" claim in the JWT is what enables this.
// Domain-wide delegation allows a Google Workspace administrator to authorize a service account to 
// act on behalf of any user in the domain, without user interaction.

// This is required for server-to-server access to user data — such as reading/sending Gmail from a background service.
// This is your company email address.
gAuth.SubEmailAddress := 'info@chilkat.xyz';

// Connect to www.googleapis.com using TLS
tlsSock := TChilkatSocket.Create(Self);
success := tlsSock.Connect('www.googleapis.com',443,1,5000);
if (success <> 1) then
  begin
    Memo1.Lines.Add(tlsSock.LastErrorText);
    Exit;
  end;

// Send the request to obtain the access token.
success := gAuth.ObtainAccessToken(tlsSock.ControlInterface);
if (success <> 1) then
  begin
    Memo1.Lines.Add(gAuth.LastErrorText);
    Exit;
  end;

// Examine the access token:
accessToken := gAuth.AccessToken;
Memo1.Lines.Add('Access Token: ' + accessToken);

// Sample output:
// ya29.a0AW4XtxjGTD67Z8 .... IRw0218

// The access token allows us to send unlimited emails while it's valid. Once it expires, we must obtain and use a new one.

// -----------------------------------------------------------------------
mailman := TChilkatMailMan.Create(Self);

// Set the properties for the GMail SMTP server:
mailman.SmtpHost := 'smtp.gmail.com';
mailman.SmtpPort := 587;
mailman.StartTLS := 1;

mailman.SmtpUsername := 'info@chilkat.xyz';
mailman.OAuth2AccessToken := accessToken;

// Create a new email object
email := TChilkatEmail.Create(Self);

email.Subject := 'This is a test';
email.Body := 'This is a test';
email.From := 'Chilkat Test <info@chilkat.xyz>';
success := email.AddTo('Chilkat Software','info@chilkatsoft.com');
// To add more recipients, call AddTo, AddCC, or AddBcc once per recipient.

success := mailman.SendEmail(email.ControlInterface);
if (success <> 1) then
  begin
    Memo1.Lines.Add(mailman.LastErrorText);
    Exit;
  end;

success := mailman.CloseSmtpConnection();
if (success <> 1) then
  begin
    Memo1.Lines.Add('Connection to SMTP server not closed cleanly.');
  end;

Memo1.Lines.Add('Successfully sent email using Gmail with a service account key.');
end;