WPSSO is multisite aware and provides a Network settings page in the Network admin interface. You can install WPSSO as a “Must Use” plugin (in the mu-plugins/ folder), Network Activate the plugin, or Activate it on individual blogs (aka sites).
Pro version licensing can be managed Network-wide, by providing a default (or forcing) the Authentication ID for Network blogs, or Authentication IDs can be entered individually on each blog’s Licenses settings page.
The default Network blog must be licensed to allow Pro version updates from the Network admin interface. This is a requirement of WordPress not WPSSO — WordPress uses the default site ID to manage updates in the network admin interface.
Blog ID 1 is usually the default Network blog, but this can be changed using a few constants in the
wp-config.php file. The default constants provided by WordPress during a multisite Network install may look like this (this is only an example – your actual network settings may differ):
define( 'MULTISITE', true );
define( 'SUBDOMAIN_INSTALL', false );
define( 'DOMAIN_CURRENT_SITE', 'example.com' );
define( 'PATH_CURRENT_SITE', '/' );
define( 'SITE_ID_CURRENT_SITE', 1 );
define( 'BLOG_ID_CURRENT_SITE', 1 );
To change the Network default blog ID, you must update the
PATH_CURRENT_SITE constants for sub-folder multisites, or
DOMAIN_CURRENT_SITE for sub-domain multisites (and
SUBDOMAIN_INSTALL would also be true in that case).