Webfinger not compatible with PHP < 8.0

[mexon]

I don't know if this is a valid bug because I'm not sure what the minimum requirements of this plugin are really supposed to be. The readme specifies PHP 5.6, and class-webfinger.php is the only place I can find a reference to str_contains. So my best theory is that this was an unintended side-effect of the fix to #152. I'm either saying that this code should be made backwards-compatible, or that the readme or other documentation should be clarified. I just don't know which.

Anyway. I access this URL on an internal test machine:

https://test1-wordpress.fritz.box/index.php?rest_route=/activitypub/1.0/webfinger&resource=acct:test@test1-wordpress.fritz.box

And I get:

Fatal error: Uncaught Error: Call to undefined function str_contains() in /srv/wordpress/test_wordpress/wp-content/plugins/activitypub/includes/rest/class-webfinger.php:47 Stack trace: #0 /usr/share/wordpress/wp-includes/rest-api/class-wp-rest-server.php(1139): Activitypub\Rest\Webfinger::webfinger() #1 /usr/share/wordpress/wp-includes/rest-api/class-wp-rest-server.php(985): WP_REST_Server->respond_to_request() #2 /srv/wordpress/test_wordpress/wp-content/plugins/activitypub/includes/rest/class-server.php(22): WP_REST_Server->dispatch() #3 /usr/share/wordpress/wp-includes/rest-api/class-wp-rest-server.php(412): Activitypub\Rest\Server->dispatch() #4 /usr/share/wordpress/wp-includes/rest-api.php(354): WP_REST_Server->serve_request() #5 /usr/share/wordpress/wp-includes/class-wp-hook.php(292): rest_api_loaded() #6 /usr/share/wordpress/wp-includes/class-wp-hook.php(316): WP_Hook->apply_filters() #7 /usr/share/wordpress/wp-includes/plugin.php(551): WP_Hook->do_action() #8 /usr/share/wordpress/wp-includes/class-wp.php(388): do_a in /srv/wordpress/test_wordpress/wp-content/plugins/activitypub/includes/rest/class-webfinger.php on line 47`

This is on Raspbian 11. PHP 7.4. Apache 2.4.54. Wordpress 5.7.5. If any of those things are not compatible, it probably should be made more clear in the readme.