filter_SSL( string $url )

Source

File: wp-includes/ms-functions.php

function filter_SSL( $url ) {  // phpcs:ignore WordPress.NamingConventions.ValidFunctionName.FunctionNameInvalid
	if ( ! is_string( $url ) ) {
		return get_bloginfo( 'url' ); // Return home blog URL with proper scheme.
	}

	if ( force_ssl_content() && is_ssl() ) {
		$url = set_url_scheme( $url, 'https' );
	}

	return $url;
}