[wp-trac] [WordPress Trac] #37616: Replace `is_super_admin()` calls with real capability checks

[WordPress Trac]

#37616: Replace `is_super_admin()` calls with real capability checks
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 Reporter:  flixos90         |      Owner:
     Type:  task (blessed)   |     Status:  new
 Priority:  normal           |  Milestone:  4.7
Component:  Role/Capability  |    Version:
 Severity:  normal           |   Keywords:
  Focuses:  multisite        |
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 As discussed in Multisite office hours
 (https://wordpress.slack.com/archives/core-multisite/p1470762377000454),
 there are plans to improve capability handling in WordPress, to also
 support network-wide (and possibly global) capabilities. The current
 `is_super_admin()` check system is no actual role- and capability-based
 system which makes it impractical to refine roles and capabilities on this
 level.

 While a super admin should have access to all capabilities, we should get
 rid of all `is_super_admin()` checks that happen outside of `WP_User` and
 the `map_meta_cap()` function and replace those calls with dedicated
 capabilities. There might be a few other occurrences where
 `is_super_admin()` is actually the right choice, but generally it
 shouldn't be used in other locations anymore. This will open up new
 possibilities to think about how we can implement a true role- and
 capability-based system beyond the scope of a site.

 The hardest part of this ticket will probably be finding names for the new
 capabilities. The good thing is that we most likely won't need to touch
 any roles or adjust `map_meta_cap()` since the new capabilities should
 only be granted to the super admin for now anyway.

 We should probably create a list of occurrences and think about names for
 the capabilities (or whether we can use existing capabilities) first.

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Ticket URL: <https://core.trac.wordpress.org/ticket/37616>
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