When an LTI launch is embedded in an iframe, navigating back from an attempt then forwards starts from scratch

numbas / numbas-lti-provider

An LTI tool provider to run Numbas exams

https://docs.numbas.org.uk/lti/en/latest/

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When an LTI launch is embedded in an iframe, navigating back from an attempt then forwards starts from scratch #266

Closed christianp closed 9 months ago

christianp commented 1 year ago

To reproduce:

use a browser where an LTI launch can open embedded in the VLE (so disable cross-site privacy protection)
open a Numbas link
start a new attempt
navigate back; you'll be shown the attempts listing
navigate forwards; you'll be shown the exam, but it'll start from scratch instead of resuming the attempt data.

christianp commented 9 months ago

I think this can also happen when the browser restarts, and restores the pages it had open.

To solve this, the SCORM model shouldn't be embedded in the page. It should do an AJAX request to get the latest SCORM model from the server - that can't be cached.