Unable to pass custom data in LTI Launch request. What is the correct way?

[oloff_b]

Hi everyone,

I am trying to pass custom data for a deep linking assignment placement. The custom data is set in the lti deep linking response, as part of the lti resource link item. Then, it needs to be available on the https://purl.imsglobal.org/spec/lti/claim/custom claim in the lti launch request to the tool.

Here is an example of what I have in the deep linking response when the assignment gets created:

...

"https://purl.imsglobal.org/spec/lti/claim/version": "1.3.0",
  "https://purl.imsglobal.org/spec/lti-dl/claim/content_items": [
    {
      "type": "ltiResourceLink",
      "title": "Test assignment",
      "text": "A test assignment",
      "url": "somelink...",
      "lineItem": {
        "scoreMaximum": "10",
        "label": "Assignment",
        "resourceId": "1234"
      },
      "window": {
        "targetName": "MyTool_1592687225123_1234",
        "windowFeatures": "menubar=yes,location=yes,status=yes,resizable=yes,scrollbars=no"
      },
      "iframe": {
        "width": 800,
        "height": 600
      },
      "custom": {
        "assignment_type": "specific_assignment_type",
        "assignment_id": "1234_5678"
      }
    }
  ]

Here is the problem: when I try to access the https://purl.imsglobal.org/spec/lti/claim/custom property in the lti launch request message, it is empty. It seems like my custom data isn't being passed in the launch request.

Does anyone know what I am doing wrong? Is this the correct way to pass custom data to the launch or is it supposed to be done differently?

I'd really appreciate any help on this.

[oloff_b · Accepted solution]

The workaround for this was to simply pass the data in the query string. E.g.

{
      "type": "ltiResourceLink",
      "title": "Test assignment",
      "text": "A test assignment",
      "url": "myResourceLink?assignment_id=1234567",
      "lineItem": {
        "scoreMaximum": "10",
        "label": "Assignment",
        "resourceId": "1234"
},

....

It seems that Canvas will only allow passing variable substitution values as custom data in the launch. This must be configured in the tool settings and cannot be modified by the tool itself in the deep link response.

[karl]

Oloff, thanks for posting the work around. For Oloff, and others who find this post, supporting custom parameters passed in deep linking messages is planned work and has been for some time. We hope to start work for this in the coming months.

[matthew_buckett]

I was reading the latest deploy notes and saw the link to the source code summary, in the document is a row titled: "add custom fields to lti resource link" which I think will allow custom fields/parameters on LTI 1.3 resource link requests.

So hopefully in the new year you won't need to use the query parameter workaround.

NB: Also it looks like Canvas is supporting LTI 1.3 tools in public courses.

[MurrayRowan]

Any update on this? I can't seem to find anything that suggests this has ever been fixed/added; maybe someone knows better though?

[matthew_buckett]

It's working for me on an Instructure supported instance. If a deep linking flow is launched from a `link_selection` placement then you can pass custom parameters as outlined in https://www.imsglobal.org/spec/lti-dl/v2p0#lti-resource-link in the deep linking response and then when the LTI tool is launched it will include the custom parameters in the launch.