CA key of EG91 module sim

Now, I am using EG91 connect to Google IOT cloud via MQTT. It maybe need vertify SSL.
How do I get CA key of EG91 module sim?
Where do I get CA key?
Please help me as soon as possible

Hello Nguy_n_Minh_Ch_ng, thanks for your question
you can get CA key via contact the MQTT server provider, thank you.