Add placeholder SAST Configration page

Part of [New SAST Config UI Page - Basic SAST Wide Settings][1].

Behind feature flag `sast_configuration_ui` (disabled by default).

[1]: https://gitlab.com/gitlab-org/gitlab/-/issues/220577

ee/app/controllers/projects/security/sast_configuration_controller.rb

@@ -3,20 +3,65 @@
 module Projects
   module Security
     class SastConfigurationController < Projects::ApplicationController
+      include CreatesCommit
       include SecurityDashboardsPermissions
 
       alias_method :vulnerable, :project
 
       before_action :ensure_sast_configuration_enabled!
+      before_action :authorize_edit_tree!, only: [:create]
 
       def show
       end
 
+      def create
+        @branch_name = project.repository.next_branch("add-sast-config")
+
+        @commit_params = {
+          commit_message: "Add .gitlab-ci.yml to enable SAST",
+          actions: [{ action: "create", file_path: ".gitlab-ci.yml", content: gitlab_ci_yml }]
+        }
+
+        project.repository.add_branch(current_user, @branch_name, project.default_branch)
+
+        create_commit(::Files::MultiService, success_notice: _("The .gitlab-ci.yml has been successfully created."),
+                      success_path: successful_change_path, failure_path: '')
+      end
+
       private
 
       def ensure_sast_configuration_enabled!
         not_found unless ::Feature.enabled?(:sast_configuration_ui, project)
       end
+
+      def successful_change_path
+        description = "Add .gitlab-ci.yml to enable SAST security scan using the GitLab managed SAST template."
+        merge_request_params = { source_branch: @branch_name, description: description }
+        project_new_merge_request_url(@project, merge_request: merge_request_params)
+      end
+
+      def gitlab_ci_yml
+        return ado_yml if project.auto_devops_enabled?
+
+        sast_yml
+      end
+
+      def ado_yml
+        <<-CI_YML.strip_heredoc
+          include:
+            - template: Auto-DevOps.gitlab-ci.yml
+        CI_YML
+      end
+
+      def sast_yml
+        <<-CI_YML.strip_heredoc
+          stages:
+            - test
+
+          include:
+            - template: SAST.gitlab-ci.yml
+        CI_YML
+      end
     end
   end
 end

ee/app/presenters/projects/security/configuration_presenter.rb

@@ -48,6 +48,7 @@ module Projects
         {
           auto_devops_enabled: auto_devops_source?,
           auto_devops_help_page_path: help_page_path('topics/autodevops/index'),
+          create_sast_merge_request_path: project_security_configuration_sast_path(project),
           features: features.to_json,
           help_page_path: help_page_path('user/application_security/index'),
           latest_pipeline_path: latest_pipeline_path,

ee/config/routes/project.rb

@@ -67,7 +67,7 @@ constraints(::Constraints::ProjectUrlConstrainer.new) do
 
           resource :configuration, only: [:show], controller: :configuration do
             post :auto_fix, on: :collection
-            resource :sast, only: [:show], controller: :sast_configuration
+            resource :sast, only: [:show, :create], controller: :sast_configuration
           end
 
           resource :discover, only: [:show], controller: :discover

ee/spec/controllers/projects/security/sast_configuration_controller_spec.rb

@@ -70,4 +70,34 @@ RSpec.describe Projects::Security::SastConfigurationController do
       end
     end
   end
+
+  describe 'POST #create' do
+    let_it_be(:project) { create(:project, :repository, namespace: group) }
+
+    before do
+      stub_licensed_features(security_dashboard: true)
+
+      sign_in(developer)
+    end
+
+    context 'with valid params' do
+      it 'returns the new merge request url' do
+        create_sast_configuration user: developer, project: project, params: {}
+
+        expect(json_response["message"]).to eq("success")
+        expect(json_response["filePath"]).to match(/#{project_new_merge_request_url(project, {})}(.*)description(.*)source_branch/)
+      end
+    end
+  end
+
+  def create_sast_configuration(user:, project:, params:)
+    post_params = {
+      namespace_id: project.namespace.to_param,
+      project_id: project.to_param,
+      sast_configuration: params,
+      format: :json
+    }
+
+    post :create, params: post_params, as: :json
+  end
 end

ee/spec/presenters/projects/security/configuration_presenter_spec.rb

@@ -28,6 +28,10 @@ RSpec.describe Projects::Security::ConfigurationPresenter do
       expect(auto_fix['container_scanning']).to be_truthy
     end
 
+    it 'includes the path to create a SAST merge request' do
+      expect(subject[:create_sast_merge_request_path]).to eq(project_security_configuration_sast_path(project))
+    end
+
     context "when the latest default branch pipeline's source is auto devops" do
       before do
         create(

locale/gitlab.pot

@@ -22928,6 +22928,9 @@ msgid_plural "The %{type} contains the following errors:"
 msgstr[0] ""
 msgstr[1] ""
 
+msgid "The .gitlab-ci.yml has been successfully created."
+msgstr ""
+
 msgid "The Advanced Global Search in GitLab is a powerful search service that saves you time. Instead of creating duplicate code and wasting time, you can now search for code within other teams that can help your own project."
 msgstr ""