Deploy key for push

I'm having a peculiar situation, but could be a useful feature. I need to app in my smartphone (Password Store for Android) push to a GitLab repo (on gitlab,com). I know his public SSH key and I want this SSH key would be able to push just one repository, improving the security. The feature proposal is: Create an option to add write access for deploy key, so you say "this key just and read, but this other key can push too". The idea is do some automatization without give access for all user's repositories.