I also had this error, but my LTI was working through D2L and Blackboard. Turns out if you're using a "Public JWK URL", Canvas expects the URL result's content-type header to be "application/json". 

Thanks for the update Matt. That code commit link was helpful. I am indeed trying to write this in LTI 1.3. We'll hold off on placing our LTI link on the Student Card for now.FWIW, a replacement varia...

I'm interested in adding a new placement on the Student Context Card for our LTI. However, the student ID is not available in the LTI launch POST data. I'm not seeing a suitable variable substitution ...

Hello all,We built an LTI which in turn uses OAuth to get the currently logged in user's info.  We use this user's OAuth access and refresh tokens to pull info about the user from the /api/v1/users/se...

I also had this error, but my LTI was working through D2L and Blackboard. Turns out if you're using a "Public JWK URL", Canvas expects the URL result's content-type header to be "application/json". 

Thanks for the update Matt. That code commit link was helpful. I am indeed trying to write this in LTI 1.3. We'll hold off on placing our LTI link on the Student Card for now.FWIW, a replacement varia...

I'm interested in adding a new placement on the Student Context Card for our LTI. However, the student ID is not available in the LTI launch POST data. I'm not seeing a suitable variable substitution ...

Hello all,We built an LTI which in turn uses OAuth to get the currently logged in user's info.  We use this user's OAuth access and refresh tokens to pull info about the user from the /api/v1/users/se...