Accessing Custom Fields from LTI 1.3 Developer Key

[KaczynskiS]

Hi, I have been working on setting up a developer key in Canvas and configuring a custom tool to support LTI 1.3. I've attempted to utilize variable substitution using the "custom_fields" field in the developer key so that I can get basic information like the name and email of the person launching the tool from Canvas, but am not seeing any of those fields showing up in the post parameters that I receive in the tool. Can anyone provide some guidance on how I should be going about accessing that data? Thanks.

[chriscas]

Hi @KaczynskiS,

I was actually just working in this area for a colleague setting up an LTI, so I have a screenshot I can share with you (no real info included here, just test stuff).  The custom parameters come through in the "https://purl.imsglobal.org/spec/lti/claim/custom" part of the LTI launch, as shown here.

For completeness, here is the developer key config for the LTI launch I captured above:

Let us know if this info helps!

-Chris

 

[KaczynskiS]

Hi Chris, 

Thanks for the quick response! I am not seeing any of the information from the LTI launch (such as that custom claim url you specified), aside from the basic post parameters containing the issuer, client id, redirect url, etc. I am wondering if I might be missing some kind of validation step or something. I have the custom fields field filled out similarly to how you showed in your screenshot so I don't think that's where my problem is coming from.

- Sarah

[chriscas]

Hi @KaczynskiS,

Are you decoding the JWT payload that the LTI 1.3 spec integration sends?  The bult of the payload for LTI 1.3 is encoded in the JWT.  If you're a chrome-based browser used, I'd highly recommend the LTI Debugger extension, which is what I was using for my screenshot.  It works in the browser developer mode to show what the LMS is sending as a payload for each launch, decoding the JWT for you, which is great to figure out whether Canvas is sending things right and your app is not decoding properly, or if Canvas itself is the issue.

Let us know if the info helps!

-Chris

[thohoangngo]

First you would need to go to the developer key,  input to the Custom Fields (Additional Settings) some thing like this:

user_id=$Canvas.user.id
user_uuid=$vnd.instructure.User.uuid

Then you could see user_id and user_uuid in the id_token returned from Canvas by a callback request

You can refer to this list for the available variables:
https://gist.github.com/jbasdf/15fb8abed66fbaf623cdfbdd45bfb1c4