Table of Contents

Overview

As of SSP v2.5.2 and v2.6.0, SSP later ships with an implementation of an IMS LTI v1.0 Tool Provider (TP). This allows for point-to-point, inbound SSO into SSP in much the same way as the legacy "Signed URL SSO" mechanism, but in a standards-compliant fashion. The LTI standard is so widely adopted that the SSP team expects LTI to quickly become SSP's most commonly used inbound SSO protocol for tool-to-tool integrations since it typically requires no custom code development.

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See here for a description of the technical implementation and more detail on the supported tool launch API.

Original JIRA ticket was:

Enabling the Tool Provider

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Tool Consumer Configuration Step 2 - Complete the LTI Consumer Creation Form

Adding a new Consumer definition defines the connection between the LTI Provider and SSP.  You will need to know the Lti person identifier and section code field in order to complete the form.  A newly defined Consumer will create the person record in the SSP database based on the Consumer Name and Key values.

• The  Consumer Name field is a friendly name to identify the Consumer
• The Consumer Key field will actually be stored in the person.username column in the SSP database. As such:
  • Expect the value you enter to be forced to lower case, and
  • Be sure to pick a value which will not conflict with a "real" end user's username
  • The TC must know what its Consumer Key is for the SSP TP. Because TP's are ultimately responsible for ensuring each real-world TC integrated with it has a unique Consumer Key, it is often up to the TP to specify to the TC what the Consumer Key should be. But this can be a collaborative process.
• The Consumer

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• Secret is also shared with and possibly arrived at via negotiation with the TC. The SSP TP implementation enforces no strength restrictions on this field other than that it must be non-empty. But in practice it should be at least as strong as whatever institutional requirements are placed on end-user passwords and likely stronger than that, since it is used for establishing an application-to-application trust relationship that allows the TC to assume the identity of any user. Because of the nature of LTI security, this value must be stored in plain text in both the TP and TC.
• Set the Lti User Id Field to the name of the LTI launch parameter in which the TC will send the launching end user's identifier. The correct value to place here may not be known until you start to experiment with the TC. (Most TC implementations offer some sort of mechanism for snooping on TP launch requests so you can see which launch parameters are being passed.)
• Use the SSP User Attribute combo box to specify the type of end user identifier SSP should expect to receive from the TC in Lti User Id Field, either username or schoolId.
• Use the Lti Section Code Field to specify the LTI launch parameter in which the TC will uniquely identify the course in which the end user was present when she initiated the launch. If the launch URL in the TC is configured to target the Early Alert portlet, the values sent in this launch parameter must match values loaded into the section_code field in external_faculty_course and external_faculty_course_roster SSP database tables.

Many of the field in the form offer additional help when you hover over field labels.

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1. Consumer Key - Configured above
2. Consumer Secret - Configured above
3. Launch URL - See below

SSP LTI Tool

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Provider Launch URLs

SSP launch URLs are of this form:

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1. https://source.sakaiproject.org/svn/basiclti/trunk/basiclti-docs/resources/docs/sakai-api-test/
2. https://github.com/csev/sakai-lti-test/

Common Problems

Offloaded SSL - If SSL connections terminate outside of Tomcat, e.g. in Apache or your load balancer, the SSP TP will refuse to authenticate launch requests unless Tomcat is tricked into thinking it is actually receiving SSL requests. This is typically done by adding the following attributes to the <Connector> in <tomcat>/conf/server.xml responsible for receiving traffic from the SSL termination point:

scheme="https" proxyPort="443" secure="true"

404 After Launch - The launch itself doesn't seem to error out and the user is redirected to a /ssp-platform URL, but gets a 404 at that location. This is often caused by one or more of the following being misconfigured in SSP_CONFIGDIR/ssp-platform-config.properties:  

environment.build.uportal.server=ssp.institution.edu
environment.build.uportal.protocol=https
environment.build.uportal.context=/ssp-platform

Launch Failures or Target Failures - Messages in the SSP log (<tomcat>/logs/ssp.log by default) should describe the technical problem associated with launch failures without requiring any special logging configuration, especially for 'test' launches. If you are not seeing such logs, try increasing the log level for the LtiLaunchErrorHandler component. In SSP_CONFIGDIR/logback.xml: 

<logger name="org.jasig.ssp.util.security.lti.LtiLaunchErrorHandler" level="warn" />

If the problem seems to have to do with the target receiving unexpected launch parameters or the launch failure suggests a problem with unexpected LTI launch parameters and the TC's request debugging tools are insufficient, try increasing logging in the OAuth package. In SSP_CONFIGDIR/logback.xml: 

<logger name="org.springframework.security.oauth" level="debug" />

In particular, look for messages containing the string "Verifying signature", which won't provide an unprocessed view onto the original launch parameters, but will give you a very good idea of what all was in the original request.

The Tomcat RequestDumperValve is another option for getting at the original request in a less processed format, although it can have side-effects which may disrupt the LTI message authentication process.

Moodle Isn't Sending the Launch Parameters I Need

OOTB, Moodle's LTI Tool Consumer does not send a value SSP can use as either a username or a schoolId. Workarounds:

1. Use Email Address Instead - Moodle does send a lis_person_contact_email_primary launch parameter which can be used to look up Platform accounts, assuming values in that field uniquely identify users in your SSP deployment. To this end, starting with SSP 2.5.3 and 2.6.0, SSP's Tool Consumer configuration UI allows you to set primaryEmailAddress in the 'SSP User Attribute' field. Use that value whenever setting 'Lti User Id Field' to lis_person_contact_email_primary. Also, if you've configured SSP Platform to source user attributes from either a custom database table or AD/LDAP, you'll likely need to add an entry to the <queryAttributeMapping> element in <platform-src>uportal-war/src/main/resources/properties/contexts/personDirectoryContext.xml: <entry key="primaryEmailAddress" value="{physical-mail-attribute-name}"/>. The local default uPortal DAO now includes that configuration for locally provisioned Platform accounts. Specifically: 

   No Format
   <entry key="primaryEmailAddress" value="mail"/>

   The correct value for physical-mail-attribute-name will depend on the details of the external attribute source with which you are integrating and may be different for each DAO. If you are currently mapping a logical attribute named primaryEmailAddress on the "value-side" of a DAO's <resultAttributeMapping> property, you should use the "key-side" of that mapping as {physical-mail-attribute-name} (this is exactly how the local default uPortal DAO is currently configured). I.e. 

   No Format
   <property name="queryAttributeMapping"> <map> <!-- snip --> <entry key="primaryEmailAddress" value="mail"/> <!-- snip --> </map> </property> <property name="resultAttributeMapping"> <map>   <!-- snip --> <entry key="mail"> <set> <value>primaryEmailAddress</value> </set> </entry> <!-- snip --> </map> </property>

2. Modify Moodle Source - To include a username in LTI launch params, edit moodle/mod/lti/locallib.php or moodle/mod/basiclti/locallib.php to add a line like the following to the block where launch parameters are assembled:

   No Format
   $requestparams['lis_person_username'] = $USER->username;

   E.g. the end result should resemble: 

   No Format
   $requestparams['lis_person_name_given'] = $USER->firstname; $requestparams['lis_person_name_family'] = $USER->lastname; $requestparams['lis_person_name_full'] = $USER->firstname." ".$USER->lastname; // Next line added to export the current user's username as a LTI launch param $requestparams['lis_person_username'] = $USER->username;

   Similar code changes may be feasible if you need to include a schoolId parameter, but the details depend on where/how exactly your Moodle instance stores that value.

OOTB, Moodle also does not necessarily send a LTI launch parameter that maps to SSP section_code in an obvious way. In some deployments the context_label launch parameter serves this purpose, but whether or not that field has the necessary semantics is very deployment specific. Some trial and error may be necessary. If no OOTB-supported launch parameters can be correctly mapped to section_code, a Moodle code patch similar to that proposed above for username may be necessary.