We've been using the 1.x version of the ims-lti gem and have decided that it's time to upgrade to the 2.0 version.
We're using this bit of code from the documentation to validate the LTI launch:
authenticator = IMS::LTI::Services::MessageAuthenticator.new(request.url, request.request_parameters, lti_secret)
Everything works great for an LTI launch from a course level navigation item - the signature is valid and everything is great.
However, if I launch the same tool for a content item selection request (i.e. as an editor button) then the signature always fails. If I walk my code back to the 1.x version of the gem everything works great again so I know that I can get a valid signature with a previous version of the gem. I'm not changing the shared secret between requests.
Any idea why the content item selection LTI launch fails?