500 Internal Server Error with LTI Public JWK URL

[svickers2]

Just a heads-up in case anyone else encounters this issue.

I was getting a 500 Internal Server Error from Canvas when a user returns from an LTI tool with an LtiDeepLinkingResponse message.  The page displayed gave no clues as to the cause, but it has subsequently transpired that it arose because Canvas was unable to verify the SSL certificate on the tool server.  Instructure support referred me to sites like https://www.ssllabs.com/ssltest/analyze.html and https://www.sslshopper.com/ssl-checker.html for checking a site's SSL certificate.  Whilst, in my case, none of my web browsers reported any issues with the SSL certificate, these sites noted some chaining issues which I assume were sufficient to cause Canvas to fall over.  For now, my workaround is to define the public JWK in the LTI Developer Key configuration in Canvas to avoid having to make this request to the server.

Happy coding!

[matthew_buckett]

Thanks for the problem report.👍

With LTI 1.3 I've found Canvas to be very unhelpful in the error messages that it gives which makes debugging integrations much harder. For things like this Canvas should really be giving a nice error to help developers progress faster.