Twilio Trust Onboard X.509

New to certificate and stuff, so bear with me :smiley:

Got my hands on some new Twilio Trust Onboard sim cards where there is an X.509 certificate to help the server authenticate the connection to the server.

When I'm reading the document I get the feeling that if it makes an HTTPS the SIM will automatically sign the request with its own certificate for authentication to the server.

But I also get the feeling that my Arduino MKRGSM1400 have to extract the certificate and then sign it with the help of the SIM card itself. And then use that to make a connection to the server?

So which is it? If it is the last one. Is that something that is supported in the LIB or done by itself when you use GPRS?