How to authenticate on a web page using private keys files?

Iam using

WebUI.uploadFile(findTestObject(‘Page’), ‘C:\\file.cer’)

But is not working.

Any ideas?, the URL is:

https://www.ventanillaunica.gob.mx/vucem/Ingreso.html

Thanks in advance.

Hello AleX,
try to use input field as object to upload file to. Not page.