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(Delphi DLL) Get GMail SMTP OAuth2 Access Token for Desktop App

Demonstrates how to get a GMail SMTP OAuth2 access token from a desktop application or script, which can be used with the XOAUTH2 authentication method.

This example requires a browser window to be displayed to allow the GMail account owner to authorize the access. The code for displaying the web browser is omitted. Suggestions for a few programming languages are provided in code comments. You'll need to find out how to display a web browser and navigate to the URL returned by the call to oauth2.StartAuth.

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;

...

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

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

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');

CkOAuth2_putCodeChallenge(oauth2,True);
CkOAuth2_putCodeChallengeMethod(oauth2,'S256');

//  This is the full-permissions scope for GMail.
CkOAuth2_putScope(oauth2,'https://mail.google.com/');

//  Begin the OAuth2 three-legged 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;

//  At this point, your application should load the URL in a browser.
//  For example,
//  in C#:  System.Diagnostics.Process.Start(url);
//  in Java: Desktop.getDesktop().browse(new URI(url));
//  in VBScript: Set wsh=WScript.CreateObject("WScript.Shell")
//               wsh.Run url
//  The Google account owner would interactively accept or deny the authorization request.

//  Add the code to load the url in a web browser here...
//  Add the code to load the url in a web browser here...
//  Add the code to load the url in a web browser here...

//  Now wait for the authorization.
//  We'll wait for a max of 30 seconds.
numMsWaited := 0;
while (numMsWaited < 30000) and (CkOAuth2_getAuthFlowState(oauth2) < 3) do
  begin
    CkOAuth2_SleepMs(oauth2,100);
    numMsWaited := numMsWaited + 100;
  end;

//  If there was no response from the browser within 30 seconds, then
//  the AuthFlowState will be equal to 1 or 2.
//  1: Waiting for Redirect. The OAuth2 background thread is waiting to receive the redirect HTTP request from the browser.
//  2: Waiting for Final Response. The OAuth2 background thread is waiting for the final access token response.
//  In that case, cancel the background task started in the call to StartAuth.
if (CkOAuth2_getAuthFlowState(oauth2) < 3) then
  begin
    CkOAuth2_Cancel(oauth2);
    Memo1.Lines.Add('No response from the browser!');
    Exit;
  end;

//  Check the AuthFlowState to see if authorization was granted, denied, or if some error occurred
//  The possible AuthFlowState values are:
//  3: Completed with Success. The OAuth2 flow has completed, the background thread exited, and the successful JSON response is available in AccessTokenResponse property.
//  4: Completed with Access Denied. The OAuth2 flow has completed, the background thread exited, and the error JSON is available in AccessTokenResponse property.
//  5: Failed Prior to Completion. The OAuth2 flow failed to complete, the background thread exited, and the error information is available in the FailureInfo property.
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;

 

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