(Delphi DLL) Refresh GMail SMTP OAuth2 Access Token

Demonstrates how to refresh an access token for sending email via GMail (SMTP).

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, OAuth2, StringBuilder, JsonObject;

...

procedure TForm1.Button1Click(Sender: TObject);
var
jsonToken: HCkJsonObject;
success: Boolean;
oauth2: HCkOAuth2;
sbJson: HCkStringBuilder;

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

// See Get GMail SMTP Access Token 
// for sample code showing how to obtain a GMail SMTP access token for desktop apps.

// It is assumed we previously obtained an OAuth2 access token for GMail (one with a scope for sending email).

jsonToken := CkJsonObject_Create();
success := CkJsonObject_LoadFile(jsonToken,'qa_data/tokens/_gmailSmtp.json');
if (success <> True) then
  begin
    Memo1.Lines.Add('Failed to load _gmailSmtp.json');
    Exit;
  end;

// The access token JSON looks something like this:

// 	{ 
// 	 "access_token": "abac.Ci-ZabcdF37-NUrmSzxbHxTsMbtlN-uPfabcdAQN_2ekzj0s5ofCzRabcdTDMGaa2Q",
// 	 "token_type": "Bearer",
// 	 "expires_in": 3600,
// 	 "refresh_token": "1/lEe5abcdNJ77eOSDBabcdkQGVmDalkwabcdR2Hatbo"
// 	}
// 

oauth2 := CkOAuth2_Create();

CkOAuth2_putTokenEndpoint(oauth2,'https://www.googleapis.com/oauth2/v4/token');

// Replace these with actual values.
CkOAuth2_putClientId(oauth2,'GOOGLE-CLIENT-ID');
CkOAuth2_putClientSecret(oauth2,'GOOGLE-CLIENT-SECRET');

// Get the "refresh_token"
CkOAuth2_putRefreshToken(oauth2,CkJsonObject__stringOf(jsonToken,'refresh_token'));

// Send the HTTP POST to refresh the access token..
success := CkOAuth2_RefreshAccessToken(oauth2);
if (success <> True) then
  begin
    Memo1.Lines.Add(CkOAuth2__lastErrorText(oauth2));
    Exit;
  end;

// The response contains a new access token, but we must keep
// our existing refresh token for when we need to refresh again in the future.
CkJsonObject_UpdateString(jsonToken,'access_token',CkOAuth2__accessToken(oauth2));

// Save the new JSON access token response to a file.
sbJson := CkStringBuilder_Create();
CkJsonObject_putEmitCompact(jsonToken,False);
CkJsonObject_EmitSb(jsonToken,sbJson);
CkStringBuilder_WriteFile(sbJson,'qa_data/tokens/_gmailSmtp.json','utf-8',False);

Memo1.Lines.Add('OAuth2 authorization granted!');
Memo1.Lines.Add('New Access Token = ' + CkOAuth2__accessToken(oauth2));

CkJsonObject_Dispose(jsonToken);
CkOAuth2_Dispose(oauth2);
CkStringBuilder_Dispose(sbJson);

end;