(Delphi ActiveX) Google Calendar -- Refresh an Expired Access Token

See more Google Calendar Examples

Demonstrates how to refresh an expired access token. If a Google Calendar REST API call results in a 401 "unauthorized" response, then it is likely the access token expired. An application should be able to automatically refresh the access token with no user interaction and then re-try the request with the newly obtained access token.

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
jsonToken: TChilkatJsonObject;
success: Integer;
oauth2: TChilkatOAuth2;
sbJson: TChilkatStringBuilder;

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

// It is assumed we previously obtained an OAuth2 access token.
// This example loads the JSON access token file 
// saved by this example: Get Google Calendar OAuth2 Access Token

jsonToken := TChilkatJsonObject.Create(Self);
success := jsonToken.LoadFile('qa_data/tokens/googleCalendar.json');
if (success <> 1) then
  begin
    Memo1.Lines.Add('Failed to load googleCalendar.json');
    Exit;
  end;

// The access token JSON looks like this:

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

oauth2 := TChilkatOAuth2.Create(Self);

oauth2.TokenEndpoint := 'https://www.googleapis.com/oauth2/v4/token';

// Replace these with actual values.
oauth2.ClientId := 'GOOGLE-CLIENT-ID';
oauth2.ClientSecret := 'GOOGLE-CLIENT-SECRET';

// Get the "refresh_token"
oauth2.RefreshToken := jsonToken.StringOf('refresh_token');

// Send the HTTP POST to refresh the access token..
success := oauth2.RefreshAccessToken();
if (success <> 1) then
  begin
    Memo1.Lines.Add(oauth2.LastErrorText);
    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.
jsonToken.UpdateString('access_token',oauth2.AccessToken);

// Save the new JSON access token response to a file.
sbJson := TChilkatStringBuilder.Create(Self);
jsonToken.EmitCompact := 0;
jsonToken.EmitSb(sbJson.ControlInterface);
sbJson.WriteFile('qa_data/tokens/googleCalendar.json','utf-8',0);

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