Expose CI secrets configuration in API response

Update `/api/v4/jobs/request` endpoint to include CI secrets
configuration if job has any and the feature is available.

Inject Vault server configuration details to CI secrets API response
when runner is requesting a job. Server details are currently fetched
from CI variables, this will be moved to DB and UI later.

Related to https://gitlab.com/gitlab-org/gitlab/-/issues/28321
and https://gitlab.com/gitlab-org/gitlab/-/issues/218746.

app/presenters/ci/build_runner_presenter.rb

@@ -118,3 +118,5 @@ module Ci
     end
   end
 end
+
+Ci::BuildRunnerPresenter.prepend_if_ee('EE::Ci::BuildRunnerPresenter')

ee/app/models/concerns/ee/ci/metadatable.rb

@@ -6,7 +6,7 @@ module EE
       extend ActiveSupport::Concern
 
       prepended do
-        delegate :secrets?, to: :metadata, prefix: false, allow_nil: true
+        delegate :secrets?, :secrets, to: :metadata, prefix: false, allow_nil: true
       end
 
       def secrets=(value)

ee/app/models/ee/ci/build.rb

@@ -20,7 +20,7 @@ module EE
       }.with_indifferent_access.freeze
 
       EE_RUNNER_FEATURES = {
-        secrets: -> (build) { build.ci_secrets_management_available? && build.secrets?}
+        vault_secrets: -> (build) { build.ci_secrets_management_available? && build.secrets?}
       }.freeze
 
       prepended do

ee/app/presenters/ee/ci/build_runner_presenter.rb

+# frozen_string_literal: true
+
+module EE
+  module Ci
+    module BuildRunnerPresenter
+      extend ActiveSupport::Concern
+
+      def secrets_configuration
+        secrets.to_h.transform_values do |secret|
+          secret['vault']['server'] = vault_server if secret['vault']
+          secret
+        end
+      end
+
+      private
+
+      def vault_server
+        @vault_server ||= {
+          'url' => variable_value('VAULT_SERVER_URL'),
+          'auth' => {
+            'name' => 'jwt',
+            'path' => 'jwt',
+            'data' => {
+              'jwt' => '${CI_JOB_JWT}',
+              'role' => variable_value('VAULT_AUTH_ROLE')
+            }.compact
+          }
+        }
+      end
+
+      def variable_value(key)
+        variables_hash[key]
+      end
+
+      def variables_hash
+        @variables_hash ||= variables.map do |variable|
+          [variable[:key], variable[:value]]
+        end.to_h
+      end
+    end
+  end
+end

ee/lib/ee/api/entities/job_request/response.rb

+# frozen_string_literal: true
+
+module EE
+  module API
+    module Entities
+      module JobRequest
+        module Response
+          extend ActiveSupport::Concern
+
+          prepended do
+            expose :secrets_configuration, as: :secrets, if: -> (build, _) { build.ci_secrets_management_available? }
+          end
+        end
+      end
+    end
+  end
+end

ee/spec/models/ci/build_spec.rb

@@ -531,13 +531,13 @@ RSpec.describe Ci::Build do
       context 'when there are secrets defined' do
         let(:secrets) { valid_secrets }
 
-        it { is_expected.to include(:secrets) }
+        it { is_expected.to include(:vault_secrets) }
       end
 
       context 'when there are no secrets defined' do
         let(:secrets) { {} }
 
-        it { is_expected.not_to include(:secrets) }
+        it { is_expected.not_to include(:vault_secrets) }
       end
     end
 
@@ -549,13 +549,13 @@ RSpec.describe Ci::Build do
       context 'when there are secrets defined' do
         let(:secrets) { valid_secrets }
 
-        it { is_expected.not_to include(:secrets) }
+        it { is_expected.not_to include(:vault_secrets) }
       end
 
       context 'when there are no secrets defined' do
         let(:secrets) { {} }
 
-        it { is_expected.not_to include(:secrets) }
+        it { is_expected.not_to include(:vault_secrets) }
       end
     end
   end

ee/spec/presenters/ci/build_runner_presenter_spec.rb

+# frozen_string_literal: true
+require 'spec_helper'
+
+RSpec.describe Ci::BuildRunnerPresenter do
+  subject(:presenter) { described_class.new(ci_build) }
+
+  describe '#secrets_configuration' do
+    let!(:ci_build) { create(:ci_build, secrets: secrets) }
+
+    context 'build has no secrets' do
+      let(:secrets) { {} }
+
+      it 'returns empty hash' do
+        expect(presenter.secrets_configuration).to eq({})
+      end
+    end
+
+    context 'build has secrets' do
+      let(:secrets) do
+        {
+          DATABASE_PASSWORD: {
+            vault: {
+              engine: { name: 'kv-v2', path: 'kv-v2' },
+              path: 'production/db',
+              field: 'password'
+            }
+          }
+        }
+      end
+
+      context 'Vault server URL' do
+        let(:vault_server) { presenter.secrets_configuration.dig('DATABASE_PASSWORD', 'vault', 'server') }
+
+        context 'VAULT_SERVER_URL CI variable is present' do
+          it 'returns the URL' do
+            create(:ci_variable, project: ci_build.project, key: 'VAULT_SERVER_URL', value: 'https://vault.example.com')
+
+            expect(vault_server.fetch('url')).to eq('https://vault.example.com')
+          end
+        end
+
+        context 'VAULT_SERVER_URL CI variable is not present' do
+          it 'returns nil' do
+            expect(vault_server.fetch('url')).to be_nil
+          end
+        end
+      end
+
+      context 'Vault auth role' do
+        let(:vault_auth_data) { presenter.secrets_configuration.dig('DATABASE_PASSWORD', 'vault', 'server', 'auth', 'data') }
+
+        context 'VAULT_AUTH_ROLE CI variable is present' do
+          it 'contains the  auth role' do
+            create(:ci_variable, project: ci_build.project, key: 'VAULT_AUTH_ROLE', value: 'production')
+
+            expect(vault_auth_data.fetch('role')).to eq('production')
+          end
+        end
+
+        context 'VAULT_AUTH_ROLE CI variable is not present' do
+          it 'skips the auth role' do
+            expect(vault_auth_data).not_to have_key('role')
+          end
+        end
+      end
+    end
+  end
+end

ee/spec/requests/api/ci/runner_spec.rb

+# frozen_string_literal: true
+
+require 'spec_helper'
+
+RSpec.describe API::Ci::Runner do
+  let_it_be(:project) { create(:project, :repository) }
+
+  describe '/api/v4/jobs' do
+    let(:runner) { create(:ci_runner, :project, projects: [project]) }
+
+    describe 'POST /api/v4/jobs/request' do
+      context 'secrets management' do
+        let(:pipeline) { create(:ci_pipeline, project: project, ref: 'master') }
+        let(:valid_secrets) do
+          {
+            DATABASE_PASSWORD: {
+              vault: {
+                engine: { name: 'kv-v2', path: 'kv-v2' },
+                path: 'production/db',
+                field: 'password'
+              }
+            }
+          }
+        end
+
+        let!(:ci_build) { create(:ci_build, pipeline: pipeline, secrets: secrets) }
+
+        context 'when secrets management feature is available' do
+          before do
+            stub_licensed_features(ci_secrets_management: true)
+          end
+
+          context 'when job has secrets configured' do
+            let(:secrets) { valid_secrets }
+
+            context 'when runner does not support secrets' do
+              it 'sets "runner_unsupported" failure reason and does not expose the build at all' do
+                request_job
+
+                expect(ci_build.reload).to be_runner_unsupported
+                expect(response).to have_gitlab_http_status(:no_content)
+              end
+            end
+
+            context 'when runner supports secrets' do
+              before do
+                create(:ci_variable, project: project, key: 'VAULT_SERVER_URL', value: 'https://vault.example.com')
+                create(:ci_variable, project: project, key: 'VAULT_AUTH_ROLE', value: 'production')
+              end
+
+              it 'returns secrets configuration' do
+                request_job_with_secrets_supported
+
+                expect(response).to have_gitlab_http_status(:created)
+                expect(json_response['secrets']).to eq(
+                  {
+                    'DATABASE_PASSWORD' => {
+                      'vault' => {
+                        'server' => {
+                          'url' => 'https://vault.example.com',
+                          'auth' => {
+                            'name' => 'jwt',
+                            'path' => 'jwt',
+                            'data' => {
+                              'jwt' => '${CI_JOB_JWT}',
+                              'role' => 'production'
+                            }
+                          }
+                        },
+                        'engine' => { 'name' => 'kv-v2', 'path' => 'kv-v2' },
+                        'path' => 'production/db',
+                        'field' => 'password'
+                      }
+                    }
+                  }
+                )
+              end
+            end
+          end
+
+          context 'job does not have secrets configured' do
+            let(:secrets) { {} }
+
+            it 'doesn not return secrets configuration' do
+              request_job_with_secrets_supported
+
+              expect(response).to have_gitlab_http_status(:created)
+              expect(json_response['secrets']).to eq({})
+            end
+          end
+        end
+
+        context 'when secrets management feature is not available' do
+          before do
+            stub_licensed_features(ci_secrets_management: false)
+          end
+
+          context 'job has secrets configured' do
+            let(:secrets) { valid_secrets }
+
+            it 'doesn not return secrets configuration' do
+              request_job_with_secrets_supported
+
+              expect(response).to have_gitlab_http_status(:created)
+              expect(json_response['secrets']).to eq(nil)
+            end
+          end
+        end
+      end
+
+      def request_job_with_secrets_supported
+        request_job info: { features: { vault_secrets: true } }
+      end
+    end
+
+    def request_job(token = runner.token, **params)
+      post api('/jobs/request'), params: params.merge(token: token)
+    end
+  end
+end

lib/api/entities/job_request/response.rb

@@ -33,3 +33,5 @@ module API
     end
   end
 end
+
+API::Entities::JobRequest::Response.prepend_if_ee('EE::API::Entities::JobRequest::Response')