Allow context qsh for Jira subscriptions json

The JSON endpoint will be requested by frontend using a JWT that
Atlassian provides via Javascript. This JWT will likely use a
context-qsh because Atlassian don't know for which
endpoint it will be used.

Read more about context JWT here:
https://developer.atlassian.com/cloud/jira/platform/understanding-jwt-for-connect-apps/

This is the second attempt to add this change. The first one
(https://gitlab.com/gitlab-org/gitlab/-/merge_requests/83836)
got reverted after an incident
(https://gitlab.com/gitlab-com/gl-infra/production/-/issues/6774)

This problem was fixed in this commit by only verifying qsh on the
index action.

app/controllers/jira_connect/application_controller.rb

@@ -22,6 +22,8 @@ class JiraConnect::ApplicationController < ApplicationController
   def verify_qsh_claim!
     payload, _ = decode_auth_token!
 
+    return if request.format.json? && payload['qsh'] == 'context-qsh'
+
     # Make sure `qsh` claim matches the current request
     render_403 unless payload['qsh'] == Atlassian::Jwt.create_query_string_hash(request.url, request.method, jira_connect_base_url)
   rescue StandardError

spec/controllers/jira_connect/subscriptions_controller_spec.rb

@@ -75,6 +75,18 @@ RSpec.describe JiraConnect::SubscriptionsController do
             expect(json_response).to include('login_path' => nil)
           end
         end
+
+        context 'with context qsh' do
+          # The JSON endpoint will be requested by frontend using a JWT that Atlassian provides via Javascript.
+          # This JWT will likely use a context-qsh because Atlassian don't know for which endpoint it will be used.
+          # Read more about context JWT here: https://developer.atlassian.com/cloud/jira/platform/understanding-jwt-for-connect-apps/
+
+          let(:qsh) { 'context-qsh' }
+
+          specify do
+            expect(response).to have_gitlab_http_status(:ok)
+          end
+        end
       end
     end
   end
@@ -102,7 +114,7 @@ RSpec.describe JiraConnect::SubscriptionsController do
     end
 
     context 'with valid JWT' do
-      let(:claims) { { iss: installation.client_key, sub: 1234 } }
+      let(:claims) { { iss: installation.client_key, sub: 1234, qsh: '123' } }
       let(:jwt) { Atlassian::Jwt.encode(claims, installation.shared_secret) }
       let(:jira_user) { { 'groups' => { 'items' => [{ 'name' => jira_group_name }] } } }
       let(:jira_group_name) { 'site-admins' }
@@ -158,7 +170,7 @@ RSpec.describe JiraConnect::SubscriptionsController do
         .stub_request(:get, "#{installation.base_url}/rest/api/3/user?accountId=1234&expand=groups")
         .to_return(body: jira_user.to_json, status: 200, headers: { 'Content-Type' => 'application/json' })
 
-      delete :destroy, params: { jwt: jwt, id: subscription.id }
+      delete :destroy, params: { jwt: jwt, id: subscription.id, format: :json }
     end
 
     context 'without JWT' do
@@ -170,7 +182,7 @@ RSpec.describe JiraConnect::SubscriptionsController do
     end
 
     context 'with valid JWT' do
-      let(:claims) { { iss: installation.client_key, sub: 1234 } }
+      let(:claims) { { iss: installation.client_key, sub: 1234, qsh: '123' } }
       let(:jwt) { Atlassian::Jwt.encode(claims, installation.shared_secret) }
 
       it 'deletes the subscription' do