Merge branch 'ci-lfs-fetch' into 'master'

Allow to fetch LFS from CI

## What does this MR do?

This adds support for fetching LFS object from CI jobs (mostly it's made for supporting GitLab CI).

## What is left?

- [x] Write tests covering a new authorization mechanism

cc @grzesiek @marin

See merge request !4465

CHANGELOG

@@ -76,6 +76,7 @@ v 8.9.0 (unreleased)
   - Pipelines can be canceled only when there are running builds
   - Allow authentication using personal access tokens
   - Use downcased path to container repository as this is expected path by Docker
+  - Allow to use CI token to fetch LFS objects
   - Custom notification settings
   - Projects pending deletion will render a 404 page
   - Measure queue duration between gitlab-workhorse and Rails

lib/gitlab/backend/grack_auth.rb

@@ -31,7 +31,7 @@ module Grack
 
       auth!
 
-      lfs_response = Gitlab::Lfs::Router.new(project, @user, @request).try_call
+      lfs_response = Gitlab::Lfs::Router.new(project, @user, @ci, @request).try_call
       return lfs_response unless lfs_response.nil?
 
       if @user.nil? && !@ci

lib/gitlab/lfs/response.rb

@@ -2,10 +2,11 @@ module Gitlab
   module Lfs
     class Response
 
-      def initialize(project, user, request)
+      def initialize(project, user, ci, request)
         @origin_project = project
         @project = storage_project(project)
         @user = user
+        @ci = ci
         @env = request.env
         @request = request
       end
@@ -189,7 +190,7 @@ module Gitlab
         return render_not_enabled unless Gitlab.config.lfs.enabled
 
         unless @project.public?
-          return render_unauthorized unless @user
+          return render_unauthorized unless @user || @ci
           return render_forbidden unless user_can_fetch?
         end
 
@@ -210,7 +211,7 @@ module Gitlab
 
       def user_can_fetch?
         # Check user access against the project they used to initiate the pull
-        @user.can?(:download_code, @origin_project)
+        @ci || @user.can?(:download_code, @origin_project)
       end
 
       def user_can_push?

lib/gitlab/lfs/router.rb

 module Gitlab
   module Lfs
     class Router
-      def initialize(project, user, request)
+      attr_reader :project, :user, :ci, :request
+
+      def initialize(project, user, ci, request)
         @project = project
         @user = user
+        @ci = ci
         @env = request.env
         @request = request
       end
@@ -80,7 +83,7 @@ module Gitlab
       def lfs
         return unless @project
 
-        Gitlab::Lfs::Response.new(@project, @user, @request)
+        Gitlab::Lfs::Response.new(@project, @user, @ci, @request)
       end
 
       def sanitize_tmp_filename(name)