Enable write to auth_keys file during restore

Fast lookup of authorized SSH keys in the database was ported to CE in
v10.4. This change adds the option to enable the setting via the restore
rake task and assumes yes if the force env variable is set.

changelogs/unreleased/enable-force-write-auth-keys-restore.yml

+---
+title: Enable the ability to use the force env for rebuilding authorized_keys during a restore
+merge_request: 21896
+author:
+type: fixed

doc/raketasks/backup_restore.md

@@ -523,7 +523,7 @@ more of the following options:
 
 - `BACKUP=timestamp_of_backup` - Required if more than one backup exists.
   Read what the [backup timestamp is about](#backup-timestamp).
-- `force=yes` - Does not ask if the authorized_keys file should get regenerated and assumes 'yes' for warning that database tables will be removed.
+- `force=yes` - Does not ask if the authorized_keys file should get regenerated and assumes 'yes' for warning that database tables will be removed, enabling the "Write to authorized_keys file" setting, and updating LDAP providers.
 
 If you are restoring into directories that are mountpoints you will need to make
 sure these directories are empty before attempting a restore. Otherwise GitLab

lib/tasks/gitlab/shell.rake

@@ -92,9 +92,11 @@ namespace :gitlab do
   def setup
     warn_user_is_not_gitlab
 
+    ensure_write_to_authorized_keys_is_enabled
+
     unless ENV['force'] == 'yes'
-      puts "This will rebuild an authorized_keys file."
-      puts "You will lose any data stored in authorized_keys file."
+      puts "This task will now rebuild the authorized_keys file."
+      puts "You will lose any data stored in the authorized_keys file."
       ask_to_continue
       puts ""
     end
@@ -118,4 +120,44 @@ namespace :gitlab do
     puts "Quitting...".color(:red)
     exit 1
   end
+
+  def ensure_write_to_authorized_keys_is_enabled
+    return if Gitlab::CurrentSettings.current_application_settings.authorized_keys_enabled
+
+    puts authorized_keys_is_disabled_warning
+
+    unless ENV['force'] == 'yes'
+      puts 'Do you want to permanently enable the "Write to authorized_keys file" setting now?'
+      ask_to_continue
+    end
+
+    puts 'Enabling the "Write to authorized_keys file" setting...'
+    Gitlab::CurrentSettings.current_application_settings.update!(authorized_keys_enabled: true)
+
+    puts 'Successfully enabled "Write to authorized_keys file"!'
+    puts ''
+  end
+
+  def authorized_keys_is_disabled_warning
+    <<-MSG.strip_heredoc
+      WARNING
+
+      The "Write to authorized_keys file" setting is disabled, which prevents
+      the file from being rebuilt!
+
+      It should be enabled for most GitLab installations. Large installations
+      may wish to disable it as part of speeding up SSH operations.
+
+      See https://docs.gitlab.com/ee/administration/operations/fast_ssh_key_lookup.html
+
+      If you did not intentionally disable this option in Admin Area > Settings,
+      then you may have been affected by the 9.3.0 bug in which the new setting
+      was disabled by default.
+
+      https://gitlab.com/gitlab-org/gitlab-ee/issues/2738
+
+      It was reverted in 9.3.1 and fixed in 9.3.3, however, if Settings were
+      saved while the setting was unchecked, then it is still disabled.
+    MSG
+  end
 end