SSO Config validation causes fatal error before metadata is saved

[Clorith]

In an environment with the plugin network enabled, entering the network settings page to provide the SSO IdP Metadata provides a broken settings page, as the SSO Config validation field expects the metadata to exist already when viewing the page.

The outcome of this is that it is impossible to save the page, so you are unable to add the metadata to resolve the issue without manually adding the sso_idp_metadata meta key and value to the wp_sitemeta database.

[Saolee]

I'm having the same issue. It appears to only occur when using PHP version >= 8.1

[Clorith]

In our case it was on an WP Engine environment, running PHP 8.0