Manual:$wgAvailableRights

<translate> Access</translate>: $wgAvailableRights
A list of available rights, in addition to the ones defined by the core.
<translate> Introduced in version:</translate>	1.13.0 (r34357)
<translate> Removed in version:</translate>	<translate> still in use</translate>
<translate> Allowed values:</translate>	(array of strings)
<translate> Default value:</translate>	`[]`
<translate> Other settings:</translate> <translate> Alphabetical</translate> \| <translate> By function</translate>

Details

The list of core user rights is defined in PermissionManager.php, $coreRights. See Manual:User rights#Adding new rights.

Extensions (until MediaWiki 1.24) use this variable instead, like:

$wgAvailableRights[] = 'ninja-powers';

<td class="mw-version-versionbox" title="<translate nowrap> The latest stable version is <tvar name=1>1.41</tvar></translate>">

<translate> ≥</translate> 1.25

<translate> MediaWiki version:</translate>

Since MediaWiki 1.25 do in extension.json :

	"AvailableRights": [
		"ninja-powers"
	],