Add custom variable com.instructure.Observee.sisIds

We're adding a custom variable substitution that returns a string of
observee's (students) SIS ids for the current user (observer), in the
context of the current course for LTI toll launches.

closes INTEROP-5940
flag=none

test-plan:
* Have an LTI tool installed in your local Canvas at a course
level that uses the new custom variable.
* Ensure that your current user is enrolled in at least section
in the course the tool is installed in.
* Launch the tool and ensure that under the custom claims you see
the observee ids variable expanded to an array that matches the
students your current user is linked in the current course.

Change-Id: Ib9d019411b991646633a4c3b7bc33ac159635379
Reviewed-on: https://gerrit.instructure.com/c/canvas-lms/+/249646
Tested-by: Service Cloud Jenkins <svc.cloudjenkins@instructure.com>
Reviewed-by: Weston Dransfield <wdransfield@instructure.com>
Reviewed-by: Xander Moffatt <xmoffatt@instructure.com>
QA-Review: Xander Moffatt <xmoffatt@instructure.com>
Product-Review: Karl Lloyd <karl@instructure.com>

doc/api/tools_variable_substitutions.md

@@ -188,6 +188,15 @@ context of the tool launch is within a course.
 ```
 [ "Section 1", "Section 5", "TA Section"]
 ```
+## com.instructure.Observee.sisIds
+returns all observee ids linked to this observer as an String separated by `,`.
+
+**Availability**: *when launched in a course*  
+**Launch Parameter**: *com_instructure_observee_sis_ids*  
+
+```
+"A123,B456,..."
+```
 ## Context.title
 The title of the context.
 

lib/lti/variable_expander.rb

@@ -178,6 +178,20 @@ module Lti
                        ENROLLMENT_GUARD,
                        default_name: 'com_instructure_user_section_names'
 
+    # returns all observee ids linked to this observer as an String separated by `,`
+    # @launch_parameter com_instructure_observee_ids
+    # @example
+    #   ```
+    #   "A123,B456,..."
+    #   ```
+    register_expansion 'com.instructure.Observee.sisIds', [],
+                        -> do
+                          observed_users = ObserverEnrollment.observed_students(@context, @current_user).keys
+                          observed_users&.collect { |user| find_sis_user_id_for(user) }&.compact&.join(',')
+                        end,
+                        COURSE_GUARD,
+                        default_name: 'com_instructure_observee_sis_ids'
+
     # The title of the context
     # @launch_parameter context_title
     # @example
@@ -1440,6 +1454,11 @@ module Lti
       @sis_pseudonym ||= SisPseudonym.for(@current_user, context, type: :trusted, require_sis: false, root_account: @root_account) if @current_user
     end
 
+    def find_sis_user_id_for(user)
+      context = @enrollment || @context
+      SisPseudonym.for(user, context, type: :trusted, require_sis: false, root_account: @root_account)&.sis_user_id
+    end
+
     def expand_substring_variables(value)
       value.to_s.scan(SUBSTRING_REGEX).inject(value) do |v, match|
         substring = "${#{match}}"

spec/lib/lti/capabilities_helper_spec.rb

@@ -115,7 +115,8 @@ module Lti
          com.instructure.Course.available_canvas_resources
          com.instructure.Person.pronouns
          com.instructure.User.observees
-         com.instructure.User.sectionNames)
+         com.instructure.User.sectionNames
+         com.instructure.Observee.sisIds)
     }
 
     describe '#supported_capabilities' do

spec/lib/lti/variable_expander_spec.rb

@@ -1111,6 +1111,59 @@ module Lti
         end
       end
 
+      describe '$com.instructure.Observee.sisIds' do
+        subject do
+          exp_hash = { observee_sis_ids: '$com.instructure.Observee.sisIds' }
+          variable_expander.expand_variables!(exp_hash)
+          exp_hash[:observee_sis_ids]
+        end
+
+        let(:student_a) { user_factory }
+        let(:student_b) { user_factory }
+        let(:student_c) { user_factory }
+        let(:observer) { user_factory }
+        let(:variable_expander) { VariableExpander.new(root_account, course, controller, current_user: observer, tool: tool) }
+        let(:context) do
+          c = variable_expander.context
+          c.save!
+          c
+        end
+
+        before do
+          managed_pseudonym(student_a, account: root_account, sis_user_id: 'SIS_A')
+          managed_pseudonym(student_b, account: root_account, sis_user_id: 'SIS_B')
+
+          context.enroll_student(student_a)
+          context.enroll_student(student_b)
+          context.enroll_student(student_c)
+
+          variable_expander.current_user = observer
+        end
+
+        context 'when the current user is observing students in the course context' do
+          before do
+            student_a_enrollment = context.enroll_user(observer, 'ObserverEnrollment')
+            student_a_enrollment.update!(associated_user_id: student_a.id)
+
+            student_b_enrollment = context.enroll_user(observer, 'ObserverEnrollment')
+            student_b_enrollment.update!(associated_user_id: student_b.id)
+
+            student_c_enrollment = context.enroll_user(observer, 'ObserverEnrollment')
+            student_c_enrollment.update!(associated_user_id: student_c.id)
+          end
+
+          it 'return an array of all student that has a SIS IDs' do
+            expect(subject).to eq 'SIS_A,SIS_B'
+          end
+        end
+
+        context 'when the current user is not observing students in the course context' do
+          it 'return a empty array of student SIS IDs' do
+            expect(subject).to be_empty
+          end
+        end
+      end
+
       context 'context is a course and there is a user' do
         let(:variable_expander) { VariableExpander.new(root_account, course, controller, current_user: user, tool: tool) }
         let(:user) { user_factory }