Lazarus Pascal

Automatically Refresh Token for 401 Unauthorized

See more Google Calendar Examples

Demonstrates how to automatically refresh an access token (without user interaction) when the token expires and a 401 Unauthorized response is received. Lazarus Pascal

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.Http,
  Chilkat.OAuth2,
  Chilkat.StringBuilder,
  Chilkat.JsonObject;

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

procedure RunDemo;
var
  success: Boolean;
  tokenFilePath: string;
  jsonToken: TJsonObject;
  http: THttp;
  jsonResponse: string;
  oauth2: TOAuth2;
  sbJson: TStringBuilder;

begin
  success := False;

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

  tokenFilePath := 'qa_data/tokens/googleCalendar.json';

  //  Get our current access token.
  jsonToken := TJsonObject.Create;
  success := jsonToken.LoadFile(tokenFilePath);
  if (jsonToken.HasMember('access_token') = False) then
    begin
      WriteLn('No access token found.');
      Exit;
    end;
  http := THttp.Create;
  http.AuthToken := jsonToken.StringOf('access_token');

  jsonResponse := http.QuickGetStr('https://www.googleapis.com/calendar/v3/users/me/calendarList');
  if (http.LastMethodSuccess <> True) then
    begin

      if (http.LastStatus <> 401) then
        begin
          WriteLn(http.LastErrorText);
          WriteLn('----');
          WriteLn(http.LastResponseBody);
          Exit;
        end;

      //  The access token must've expired. 
      //  Refresh the access token and then retry the request.
      oauth2 := TOAuth2.Create;

      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 <> True) then
        begin
          WriteLn(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 := TStringBuilder.Create;
      jsonToken.EmitCompact := False;
      jsonToken.EmitSb(sbJson);
      sbJson.WriteFile(tokenFilePath,'utf-8',False);

      WriteLn('OAuth2 authorization granted!');
      WriteLn('New Access Token = ' + oauth2.AccessToken);

      //  re-try the original request.
      http.AuthToken := oauth2.AccessToken;
      jsonResponse := http.QuickGetStr('https://www.googleapis.com/calendar/v3/users/me/calendarList');
      if (http.LastMethodSuccess <> True) then
        begin
          WriteLn(http.LastErrorText);
          Exit;
        end;
    end;

  WriteLn(jsonResponse);
  WriteLn('-----------------------------');


  jsonToken.Free;
  http.Free;
      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.