HTTP POST request in Inno Setup Script

Based on jsobo advice of using WinHTTP library, I came with this very simple code that does the trick. Say, you want to send serial number for verification just before the actual installation starts. In the Code section, put:

procedure CurStepChanged(CurStep: TSetupStep);
var
  WinHttpReq: Variant;
begin
  if CurStep = ssInstall then
  begin
    if AutoCheckRadioButton.Checked = True then
    begin
      WinHttpReq := CreateOleObject('WinHttp.WinHttpRequest.5.1');
      WinHttpReq.Open('POST', '<your_web_server>', false);
      WinHttpReq.SetRequestHeader('Content-Type', 'application/x-www-form-urlencoded');
      WinHttpReq.Send('<your_data>');
      { WinHttpReq.ResponseText will hold the server response }
    end;
  end;
end;

The Open method takes as arguments the HTTP method, the URL and whether to do async request and it seems like we need to add SetRequestHeader in order to set the Content-Type header to application/x-www-form-urlencoded.

WinHttpReq.Status will hold the response code, so to check if the server returned successfully:

if WinHttpReq.Status <> 200 then
begin
  MsgBox('ERROR', mbError, MB_OK);
end
else
begin
  MsgBox('SUCCESS', mbInformation, MB_OK);
end;

https://docs.microsoft.com/en-us/windows/win32/winhttp/winhttprequest lists all methods and properties of the WinHttpRequest object.

Also, to avoid run-time errors (can happen if the host is unreachable) it is a good idea to surround the code with try/except code.