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

uses
    Winapi.Windows, Winapi.Messages, System.SysUtils, System.Variants, System.Classes, Vcl.Graphics,
    Vcl.Controls, Vcl.Forms, Vcl.Dialogs, Vcl.StdCtrls, MailMan, FileAccess, AuthGoogle, Email, Socket;

...

procedure TForm1.Button1Click(Sender: TObject);
var
fac: HCkFileAccess;
jsonKey: PWideChar;
gAuth: HCkAuthGoogle;
tlsSock: HCkSocket;
success: Boolean;
accessToken: PWideChar;
mailman: HCkMailMan;
email: HCkEmail;

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 := CkFileAccess_Create();
jsonKey := CkFileAccess__readEntireTextFile(fac,'qa_data/googleApi/chilkat25-b4214220e565.json','utf-8');
if (CkFileAccess_getLastMethodSuccess(fac) <> True) then
  begin
    Memo1.Lines.Add(CkFileAccess__lastErrorText(fac));
    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 := CkAuthGoogle_Create();
CkAuthGoogle_putJsonKey(gAuth,jsonKey);

// Specify a scope.
CkAuthGoogle_putScope(gAuth,'https://mail.google.com/');

// Request an access token that is valid for this many seconds.
CkAuthGoogle_putExpireNumSeconds(gAuth,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.
CkAuthGoogle_putSubEmailAddress(gAuth,'info@chilkat.xyz');

// Connect to www.googleapis.com using TLS
tlsSock := CkSocket_Create();
success := CkSocket_Connect(tlsSock,'www.googleapis.com',443,True,5000);
if (success <> True) then
  begin
    Memo1.Lines.Add(CkSocket__lastErrorText(tlsSock));
    Exit;
  end;

// Send the request to obtain the access token.
success := CkAuthGoogle_ObtainAccessToken(gAuth,tlsSock);
if (success <> True) then
  begin
    Memo1.Lines.Add(CkAuthGoogle__lastErrorText(gAuth));
    Exit;
  end;

// Examine the access token:
accessToken := CkAuthGoogle__accessToken(gAuth);
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 := CkMailMan_Create();

// Set the properties for the GMail SMTP server:
CkMailMan_putSmtpHost(mailman,'smtp.gmail.com');
CkMailMan_putSmtpPort(mailman,587);
CkMailMan_putStartTLS(mailman,True);

CkMailMan_putSmtpUsername(mailman,'info@chilkat.xyz');
CkMailMan_putOAuth2AccessToken(mailman,accessToken);

// Create a new email object
email := CkEmail_Create();

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

success := CkMailMan_SendEmail(mailman,email);
if (success <> True) then
  begin
    Memo1.Lines.Add(CkMailMan__lastErrorText(mailman));
    Exit;
  end;

success := CkMailMan_CloseSmtpConnection(mailman);
if (success <> True) 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.');

CkFileAccess_Dispose(fac);
CkAuthGoogle_Dispose(gAuth);
CkSocket_Dispose(tlsSock);
CkMailMan_Dispose(mailman);
CkEmail_Dispose(email);

end;