I am working with an LTI vendor and want to pass them our integration_id for each student on launch. We have tried setting the custom fields to "integration_id=$Canvas.user.integration_id", but that doesn't seem to work. Can anyone tell me whether it's possible to pass the integration_id to an LTI? If it is possible, could you tell me how to do it? If it's not possible, what information can I pass to an LTI?