Error: “Can’t reach CAS server”

“Can’t reach CAS server” on the WP.com “Business” subscription plan.

Authorizer v2.9.13

Went so far as to add the following to public function admin_notices() in the class-admin-page.php file:

$response      = wp_remote_get( $cas_url );
$response_code = wp_remote_retrieve_response_code( $response );

and

<p>CAS URL:<br><pre><?php printf("%s", $cas_url ); ?></pre></p>
<p>Response Code:<br><pre><?php printf("%s", $response_code); ?></pre></p>

With that, WP.com gives me no Response Code at all, but another 3rd-party service gives me 200.

See screenshot:

View post on imgur.com

Any ideas as to what would be stopping it?