How to set custom URL for twitter card image

Hi there,

I am creating my first post with Ghost. I have my own CDN server to host images and I would like to use an image there for Twitter card as well. When I open Twitter card section in the post, it only allows me to either upload an image, or choose an image from Unsplash.

Does anyone know how I can set the image to my own CDN one? I can use SQL as well if necessary. Many thanks!!!