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LTI Launch fails for content item selection with latest IMS-LTI gem

Question asked by Justin Ball on Jun 21, 2017
Latest reply on Jun 21, 2017 by Justin Ball

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)
authenticator.valid_signature?

 

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?

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