LTI 1.3 tool has different subject claim for the same user.
We have a LTI 1.3 tool that is currently deployed in the Course Navigation placement and we were looking at also deploying it in the User Navigation placement by adding an additional placement to the LTI Developer Key. This all works fine, however when the tool launch happens the "sub" (subject) claim in the JWT is different depending on the placement.
The same user when launching the tool from multiple different courses with the same placement is always identified with the same "sub" claim.
The same user when launching the tool from different placements (even within the course, eg Course Navigation and Course Home Sub Navigation) gets a different "sub" claim.
To me this seems like a bug as it means without asking for custom fields in the LTI configuration we can't identify if it's the same user using the tool between placements.
I could understand this happening if we had multiple developer keys (but we don't). Has anyone else found this? Is there any way to get the tool to use the same "sub" claim?