InApp Soap Calls (xmlHttpRequest) with a Client Certificate

I write an app who connect to external Soap Services directly. It works. I call services from the device directly to the HTTPS Soap Server.
But now i need to encrypt the calls with a client side certificate. I have this certificate in PEM format, i know how to write in on the device disk.
Like in PHP

new SoapClient(
array( 'local_cert' => 'certificat_soap.pem',
         'connection_timeout' => 10 )

i need to call the services with the certificate… in JS… in ionic App

I don’t have a server between the app and the final Soap Server and i can’t do that. It’s the first rule of this project. The app have to speak directly with the soap server.

I’m looking for this since 3 weeks without success. Please help me.

How are you calling SOAP Services from your ionic app using xmlhttprequest