We've finished some initial development to support multiple deep link returns to Canvas for non-graded items via Modules. This is working through the process to deploy out to the beta environment with our next release. Custom parameter support for deep link requests is planned, it's just not scoped and scheduled yet. These are the two optional items from the specification we are seeing the most interest in at the moment. We're also working through requirements to provide a migration path from LTI v1.1 to v1.3 in Canvas.
Hi Dave - apologies for the delay - have you seen this library? GitHub - IMSGlobal/lti-1-3-php-library
We made a video recently featuring Martin Lenord of Turnitin who shows how to use the library to do assignment and grades as part of our LTI Spotlight video series here. You can find links and more details here: https://www.youtube.com/watch?v=YOg_mZ6bWXg&feature=youtu.be
And there is also the ceLTIc Project's PHP library for LTI which has been updated to include support for LTI 1.3/Advantage. It can be found at github.com/celtic-project/LTI-PHP/ and has a sample app to illustrate its use.