User getting blank screen when launching LTI app

[phesse]

I have just deployed an LTI app to our production environment. It works fine for me and other admins, but non-admin users get only a blank screen. When one of our admins masquerades as a user and tries it, it works for them. 

Are there any settings in Canvas that need to be made for non-admin users, so that this screen will work for them?

[justinball]

Check the tool setup and make sure visibility is set to "public" and not "admins". If that's set correctly then check to see if your LTI application use cookies (or sessions which frequently use cookies). Some browsers won't let you write a cookie if you've never visited the website outside of an iframe. Also, check your console for errors to see if there's a Javascript problem. Sometimes the code for an application will depend on the roles for a given user. That's just a guess though since I don't know what the tool is doing.

Best,

Justin

[phesse]

No cookies in the LTI app. Can you be more  specific about "tool setup"? I've looked through the entire 'Settings' and can't find anything labeled 'Visibility'. Also please go into more detail about checking my console. Thanks.

[justinball]

When we setup our tools we use the XML configuration. I've attached an example below. There's a property with the name "visibility" that can be set to admin or public. Given that admins are seeing the application but other users are not I would have guessed that the visibility was set to admin.

If you're using Chrome then go check the console in your browser just right click on the and select "inspect". In the window that opens look for Javascript errors.

<?xml version="1.0" encoding="UTF-8"?>
<cartridge_basiclti_link xmlns="http://www.imsglobal.org/xsd/imslticc_v1p0" xmlns:blti="http://www.imsglobal.org/xsd/imsbasiclti_v1p0" xmlns:lticm="http://www.imsglobal.org/xsd/imslticm_v1p0" xmlns:lticp="http://www.imsglobal.org/xsd/imslticp_v1p0" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xsi:schemaLocation="http://www.imsglobal.org/xsd/imslticc_v1p0 http://www.imsglobal.org/xsd/lti/ltiv1p0/imslticc_v1p0.xsd http://www.imsglobal.org/xsd/imsbasiclti_v1p0 http://www.imsglobal.org/xsd/lti/ltiv1p0/imsbasiclti_v1p0p1.xsd http://www.imsglobal.org/xsd/imslticm_v1p0 http://www.imsglobal.org/xsd/lti/ltiv1p0/imslticm_v1p0.xsd http://www.imsglobal.org/xsd/imslticp_v1p0 http://www.imsglobal.org/xsd/lti/ltiv1p0/imslticp_v1p0.xsd">
  <blti:title>LTI Starter App</blti:title>
  <blti:description>The Atomic Jolt LTI Starter app</blti:description>
  <blti:launch_url>https://atomicjolt-helloworld.atomicjolt.xyz/lti_launches</blti:launch_url>
  <blti:secure_launch_url>https://atomicjolt-helloworld.atomicjolt.xyz/lti_launches</blti:secure_launch_url>
  <blti:icon>https://atomicjolt-helloworld.atomicjolt.xyz/oauth_icon.png</blti:icon>
  <blti:extensions platform="canvas.instructure.com">
    <lticm:options name="assignment_selection">
      <lticm:property name="message_type">ContentItemSelectionRequest</lticm:property>
      <lticm:property name="selection_height">800</lticm:property>
      <lticm:property name="selection_width">892</lticm:property>
      <lticm:property name="text">LTI Starter App - Content Item Select</lticm:property>
      <lticm:property name="url">https://atomicjolt-helloworld.atomicjolt.xyz/lti_launches</lticm:property>
    </lticm:options>
    <lticm:options name="course_navigation">
      <lticm:property name="default">enabled</lticm:property>
      <lticm:property name="text">LTI Starter App</lticm:property>
      <lticm:property name="url">https://atomicjolt-helloworld.atomicjolt.xyz/lti_launches</lticm:property>
      <lticm:property name="visibility">public</lticm:property>
    </lticm:options>
    <lticm:options name="custom_fields">
      <lticm:property name="canvas_course_id">$Canvas.course.id</lticm:property>
    </lticm:options>
    <lticm:property name="domain">atomicjolt-helloworld.atomicjolt.xyz</lticm:property>
    <lticm:options name="editor_button">
      <lticm:property name="icon_url">https://atomicjolt-helloworld.atomicjolt.xyz/atomicjolt.png</lticm:property>
      <lticm:property name="message_type">ContentItemSelectionRequest</lticm:property>
      <lticm:property name="selection_height">800</lticm:property>
      <lticm:property name="selection_width">892</lticm:property>
      <lticm:property name="text">LTI Starter App - Content Item Select</lticm:property>
      <lticm:property name="url">https://atomicjolt-helloworld.atomicjolt.xyz/lti_launches</lticm:property>
      <lticm:property name="visibility">admins</lticm:property>
    </lticm:options>
    <lticm:options name="link_selection">
      <lticm:property name="message_type">ContentItemSelectionRequest</lticm:property>
      <lticm:property name="selection_height">800</lticm:property>
      <lticm:property name="selection_width">892</lticm:property>
      <lticm:property name="text">LTI Starter App - Content Item Select</lticm:property>
      <lticm:property name="url">https://atomicjolt-helloworld.atomicjolt.xyz/lti_launches</lticm:property>
    </lticm:options>
    <lticm:property name="privacy_level">public</lticm:property>
  </blti:extensions>
</cartridge_basiclti_link>
‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍

[phesse]

Ours was set to 'admin'. I changed it now to 'public'. We'll see if we get any reports of errors now.

Thanks!!!

[RobDitto]

 @phesse , by any chance, are the non-admin users all using the Safari browser with default "Allow from websites I visit" setting for cookie policy? We've seen the blank screen before in that scenario.  

LTI tool providers ideally will accommodate Apple's different implementation of cookie policy by rendering a minimal interface which users interact with in order to set a persistent cookie and reload the page.  After that reload, the LTI tool can look for the persistent cookie and set up a session.

To work around this without the LTI tool being changed, you could advise users to switch to "Always allow" or to try a different browser.

[phesse]

Thanks for the tip. I have sent out a notice to our users who use Safari to try this.

[phesse]

Today is the first day of classes and we're getting reports that the attendance app is not working. A more serious issue has arisen, however. Apparently, students can access this app and are able to take attendance! Obviously we don't want them to have this functionality. Did changing the visibility of the app from 'Admin' to 'Public' do this? And if so, how can we rectify it?

[justinball]

Hi Peter,

Changing from admin to public will allow all users to see the tool so you'll want to change it back to admin. What attendance app are you using? Is this Instructure's application or a different application? Even if the visibility is public the application should check the user's role from the LTI launch to ensure the user has the right to take attendance.

[phesse]

Thanks Justin. Not all our faculty are admins, so we have to leave it at public. But I am working on blocking any non-faculty from getting into the tool. 

[justinball]

I think that 'admin' should include faculty so thinking back to the original problem I find it strange that the tool wasn't visible for some faculty when it was set to admin. I wonder if there's something odd going on inside the tool. I don't have access to the code so I couldn't say for sure, but it would be worth having your tech team or the vendor debug into the LTI launch to see what's going on.

[phesse]

Actually, we never got reports from any faculty that they couldn't see the app. We just assumed that the "admin" in visibility was of the same context as "admin" privileges, that I and other techies have. Since this is not the case, and setting visibility to "admin" will shield the app from students but not faculty, I'm going to change it back to "admin". Thanks again!

PS In answer to your previous question, it's a home-grown attendance app. 

[baldwinsh]

Yesterday I was adding an LTI to a Canvas page and when I saved the LTI to the Canvas assignment page, the content on the page disappeared and the points changed from 30 to 100. I reached out to the LTI's vendor and was told that this began three months ago with a Canvas update. Is there something that the Vendor needs to do differently or is there something that users of Canvas need to do differently?