Save user ID and username in Grape API log (api_json.log)

This will enable admins to identify who actually made the API request.

Relates to #36960

changelogs/unreleased/sh-store-user-in-api-logs.yml

+---
+title: Save user ID and username in Grape API log (api_json.log)
+merge_request:
+author:
+type: changed

lib/api/api.rb

@@ -13,7 +13,8 @@ module API
         formatter: Gitlab::GrapeLogging::Formatters::LogrageWithTimestamp.new,
         include: [
           GrapeLogging::Loggers::FilterParameters.new,
-          GrapeLogging::Loggers::ClientEnv.new
+          GrapeLogging::Loggers::ClientEnv.new,
+          Gitlab::GrapeLogging::Loggers::UserLogger.new
         ]
     allow_access_with_scope :api

lib/api/helpers.rb

@@ -5,6 +5,7 @@ module API
     SUDO_HEADER = "HTTP_SUDO".freeze
     SUDO_PARAM = :sudo
+    API_USER_ENV = 'gitlab.api.user'.freeze
     def declared_params(options = {})
       options = { include_parent_namespaces: false }.merge(options)
@@ -48,10 +49,16 @@ module API
       validate_access_token!(scopes: scopes_registered_for_endpoint) unless sudo?
+      save_current_user_in_env(@current_user) if @current_user
+
       @current_user
     end
     # rubocop:enable Gitlab/ModuleWithInstanceVariables
+    def save_current_user_in_env(user)
+      env[API_USER_ENV] = { user_id: user.id, username: user.username }
+    end
+
     def sudo?
       initial_current_user != current_user
     end

lib/gitlab/grape_logging/loggers/user_logger.rb

+# This grape_logging module (https://github.com/aserafin/grape_logging) makes it
+# possible to log the user who performed the Grape API action by retrieving
+# the user context from the request environment.
+module Gitlab
+  module GrapeLogging
+    module Loggers
+      class UserLogger < ::GrapeLogging::Loggers::Base
+        def parameters(request, _)
+          params = request.env[::API::Helpers::API_USER_ENV]
+
+          return {} unless params
+
+          params.slice(:user_id, :username)
+        end
+      end
+    end
+  end
+end

spec/requests/api/helpers_spec.rb

@@ -68,6 +68,12 @@ describe API::Helpers do
           end
           it { is_expected.to eq(user) }
+
+          it 'sets the environment with data of the current user' do
+            subject
+
+            expect(env[API::Helpers::API_USER_ENV]).to eq({ user_id: subject.id, username: subject.username })
+          end
         end
         context "HEAD request" do