Delphi DLL

Get GMail SMTP OAuth2 Access Token for Desktop App

See more OAuth2 Examples

This example show how to obtain a Gmail SMTP OAuth2 access token from a desktop application or script, enabling the use of XOAUTH2 authentication. Delphi DLL

uses
    Winapi.Windows, Winapi.Messages, System.SysUtils, System.Variants, System.Classes, Vcl.Graphics,
    Vcl.Controls, Vcl.Forms, Vcl.Dialogs, Vcl.StdCtrls, OAuth2, StringBuilder;

...

procedure TForm1.Button1Click(Sender: TObject);
var
success: Boolean;
oauth2: HCkOAuth2;
url: PWideChar;
numMsWaited: Integer;
sbJson: HCkStringBuilder;

begin
success := False;

// To further clarify, see OAuth 2.0 Authorization Flow

oauth2 := CkOAuth2_Create();

// For Google OAuth2, set the listen port equal to the port used
// in the Authorized Redirect URL for the Client ID.
// For example, in this case the Authorized Redirect URL would be http://localhost:55568/
// Your app should choose a port not likely not used by any other application.
CkOAuth2_putListenPort(oauth2,55568);

CkOAuth2_putAuthorizationEndpoint(oauth2,'https://accounts.google.com/o/oauth2/v2/auth');
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');

// To use Gmail's OAuth2 for sending emails via the SMTP protocol, you need to request the https://mail.google.com/ scope. 
// See About GMail SMTP OAuth2 Scopes
CkOAuth2_putScope(oauth2,'https://mail.google.com/');

// Begin the OAuth2 Authorization code flow.  This returns a URL that should be loaded in a browser.
url := CkOAuth2__startAuth(oauth2);
if (CkOAuth2_getLastMethodSuccess(oauth2) <> True) then
  begin
    Memo1.Lines.Add(CkOAuth2__lastErrorText(oauth2));
    Exit;
  end;

// Launch the default browser on the system and navigate to the url.
// The LaunchBrowser method was added in Chilkat v10.1.2.
success := CkOAuth2_LaunchBrowser(oauth2,url);
if (success = False) then
  begin
    Memo1.Lines.Add(CkOAuth2__lastErrorText(oauth2));
    Exit;
  end;

// Wait for the user to approve or deny authorization in the browser.
numMsWaited := 0;
while (numMsWaited < 90000) and (CkOAuth2_getAuthFlowState(oauth2) < 3) do
  begin
    CkOAuth2_SleepMs(oauth2,100);
    numMsWaited := numMsWaited + 100;
  end;

// If the browser does not respond within the specified time, AuthFlowState will be:
// 
// 1: Waiting for Redirect – The OAuth2 background thread is waiting for the browser's redirect request.
// 2: Waiting for Final Response – The thread is awaiting the final access token response.
// In either case, cancel the background task initiated by StartAuth.

if (CkOAuth2_getAuthFlowState(oauth2) < 3) then
  begin
    CkOAuth2_Cancel(oauth2);
    Memo1.Lines.Add('No response from the browser!');
    Exit;
  end;

// Check AuthFlowState to determine if authorization was granted, denied, or failed:
// 
// 3: Success – OAuth2 flow completed, the background thread exited, and the successful response is in AccessTokenResponse.
// 4: Access Denied – OAuth2 flow completed, the background thread exited, and the error response is in AccessTokenResponse.
// 5: Failure – OAuth2 flow failed before completion, the background thread exited, and error details are in FailureInfo.

if (CkOAuth2_getAuthFlowState(oauth2) = 5) then
  begin
    Memo1.Lines.Add('OAuth2 failed to complete.');
    Memo1.Lines.Add(CkOAuth2__failureInfo(oauth2));
    Exit;
  end;

if (CkOAuth2_getAuthFlowState(oauth2) = 4) then
  begin
    Memo1.Lines.Add('OAuth2 authorization was denied.');
    Memo1.Lines.Add(CkOAuth2__accessTokenResponse(oauth2));
    Exit;
  end;

if (CkOAuth2_getAuthFlowState(oauth2) <> 3) then
  begin
    Memo1.Lines.Add('Unexpected AuthFlowState:' + IntToStr(CkOAuth2_getAuthFlowState(oauth2)));
    Exit;
  end;

// Save the full JSON access token response to a file.
sbJson := CkStringBuilder_Create();
CkStringBuilder_Append(sbJson,CkOAuth2__accessTokenResponse(oauth2));
CkStringBuilder_WriteFile(sbJson,'qa_data/tokens/_gmailSmtp.json','utf-8',False);

// The saved JSON response looks like this:

// 	{
// 	 "access_token": "ya39.Ci-XA_C5bGgRDC3UaD-h0_NeL-DVIQnI2gHtBBBHkZzrwlARkwX6R3O0PCDEzRlfaQ",
// 	 "token_type": "Bearer",
// 	 "expires_in": 3600,
// 	 "refresh_token": "1/r_2c_7jddspcdfesrrfKqfXtqo08D6Q-gUU0DsdfVMsx0c"
// 	}
// 
Memo1.Lines.Add('OAuth2 authorization granted!');
Memo1.Lines.Add('Access Token = ' + CkOAuth2__accessToken(oauth2));

CkOAuth2_Dispose(oauth2);
CkStringBuilder_Dispose(sbJson);

end;