Override LTI launch parameters

[estevebadia]

It would be very useful for us to be able to override the LTI parameters this plugin is sending to Kaltura in a similar way the core LTI activity plugin allows parameter overrides.

Kaltura plugin sends the Moodle username as the LTI user_id parameter. In our setting, users access Kaltura media either through Moodle and through a different platform. From our second platform we can't know Moodle usernames so we'd like to change the user_id that Moodle is sending to Kaltura via LTI so they both match.

The core LTI activity module provides the before_launch callback that allow subplugins -called ltisource plugins- to override LTI params (example of ltisource plugins). We could call the same before_launch or a custom before_kaltura_launch callback from this kaltura plugin to give other plugins the opportunity to override LTI parameters as in the core LTI module.

We're willing to develop this feature and provide a PR if you are open to accept this feature. Thank you!

[estevebadia]

Just in case this is of interest to Kaltura plugin maintainers or anyone else, we've implemented this feature by adding the following lines to the file local/kaltura/locallib.php in function local_kaltura_request_lti_launch before the call to lti_sign_parameters.

    // Call plugins of type ltisource providing the before_launch hook
    // implementation the same way it is done by Moodle's LTI mod.
    $callbacks = get_plugin_list_with_function('ltisource', 'before_launch');
    foreach ($callbacks as $plugin => $function) {
        $pluginparams = component_callback($plugin, 'before_launch', [$lti, $endpoint, $requestparams], []);
        if (!empty($pluginparams) && is_array($pluginparams)) {
            $requestparams = array_merge($requestparams, $pluginparams);
        }
    }

I'll be happy to provide a PR to your branches if you're willing to accept this.