Check alerts service token properly

Fixes https://gitlab.com/gitlab-org/gitlab/issues/14792

Check the token generated by alerts service
instead of checking with a hard-coded value

ee/app/services/projects/alerting/notify_service.rb

@@ -5,11 +5,6 @@ module Projects
     class NotifyService < BaseService
       include Gitlab::Utils::StrongMemoize
 
-      # Prevents users to use WIP feature on private GitLab instances
-      # by enabling 'generic_alert_endpoint' feature manually.
-      # TODO: https://gitlab.com/gitlab-org/gitlab/issues/14792
-      DEV_TOKEN = :development_token
-
       def execute(token)
         return forbidden unless alerts_service_activated?
         return unauthorized unless valid_token?(token)
@@ -23,6 +18,8 @@ module Projects
 
       private
 
+      delegate :alerts_service, to: :project
+
       def generic_alert_endpoint_enabled?
         Feature.enabled?(:generic_alert_endpoint, project)
       end
@@ -34,7 +31,7 @@ module Projects
       def alerts_service_activated?
         incident_management_available? &&
           generic_alert_endpoint_enabled? &&
-          project.alerts_service.try(:active?)
+          alerts_service.try(:active?)
       end
 
       def process_incident_issues
@@ -47,7 +44,7 @@ module Projects
       end
 
       def valid_token?(token)
-        token == DEV_TOKEN
+        token == alerts_service.token
       end
 
       def bad_request

ee/spec/services/projects/alerting/notify_service_spec.rb

@@ -36,7 +36,7 @@ describe Projects::Alerting::NotifyService do
   end
 
   describe '#execute' do
-    let(:token) { :development_token }
+    let(:token) { 'invalid-token' }
     let(:starts_at) { Time.now.change(usec: 0) }
     let(:service) { described_class.new(project, nil, payload) }
     let(:payload_raw) do
@@ -63,6 +63,8 @@ describe Projects::Alerting::NotifyService do
           let!(:alerts_service) { create(:alerts_service, project: project) }
 
           context 'with valid token' do
+            let(:token) { alerts_service.token }
+
             context 'with a valid payload' do
               it_behaves_like 'processes incident issues', 1
             end
@@ -79,8 +81,6 @@ describe Projects::Alerting::NotifyService do
           end
 
           context 'with invalid token' do
-            let(:token) { 'invalid-token' }
-
             it_behaves_like 'does not process incident issues', http_status: 401
           end
         end