Add support for remote launch url

[miguelwicht]

These changes allow the plugin to launch content that is hosted on a remote system and provide a way to implement some kind of authorization via the GET parameters e.g. by signing the launch url.

[miguelwicht]

@davidpesce Any chance this will get reviewed and merged? Happy to answer questions if there are any.

[davidpesce]

Hi @miguelwicht - Sorry for the late reply, I haven't had a chance to look into this. That said, the current plugin does allow launching of remote content.

[miguelwicht]

@davidpesce I took another look and launching remote content does indeed work but only if you manually enter the launch url and activity Id in the form. If you try to set them via the tincan.xml file it does not because the plugin prepends the launch url with something like this: "http://moodle.docker.localhost/pluginfile.php/18/mod_tincanlaunch/content/" where "http://moodle.docker.localhost" is the url of your Moodle instance. That is why I added the check for a valid URL before updating the launch url.

This was kinda hard to debug because after the plugin prepended the string to the URL my links exceeded the 255 character limit and the returned error and link mentioned a completely unrelated problem.