Implement some form of logging

[daledavies]

Most basic level, an event logs details of which rule plugins denied access and when.

We could pass the rule plugin types as debug data to the event in a similar way to what tool_mfa does...

public static function user_failed_mfa_event($user) {
        // Build debug info string.
        $factors = \tool_mfa\plugininfo\factor::get_active_user_factor_types();
        $debug = '';
        $failurereason = get_string('event:failnotenoughfactors', 'tool_mfa');
        foreach ($factors as $factor) {
            $debug .= "<br> Factor {$factor->name} status: {$factor->get_state()}";
            if ($factor->get_state() === \tool_mfa\plugininfo\factor::STATE_FAIL) {
                $failurereason = get_string('event:failfactor', 'tool_mfa');
            } else if ($factor->get_state() === \tool_mfa\plugininfo\factor::STATE_LOCKED) {
                $failurereason = get_string('event:faillockout', 'tool_mfa');
            }
        }

        $data = [
            'relateduserid' => null,
            'context' => \context_user::instance($user->id),
            'other' => [
                'userid' => $user->id,
                'debug' => $debug,
                'failurereason' => $failurereason,
            ],
        ];

        return self::create($data);
    }