Programatically define Menu links
If you are creating a menu link from a custom module, you can check this 

https://www.drupal.org/docs/8/api/routing-system/structure-of-routes

Quoting the documentation:

requirements (required): Determines what must be met in order to grant access to the route. 
    _role: A specific Drupal role, eg. 'anonymous'. 


Alternatively you can use this module: https://www.drupal.org/project/menu_item_visibility
"It exposes configurable and extendable visibility settings for menu links."