Saving Image to Camera Roll

Hi, I’m making a wallpaper app for learning purposes and i was wondering how i could do something. How do i save a image that i load from my server into a users camera roll ? Like saving the image file if they click a button to save that selected wallpaper.

Thank you.

Looks like the Ionic team built a plug-in for this: https://github.com/driftyco/cordova-camera-roll