Backport option to disable writing to `authorized_keys` file

Originally branch 'mk-toggle-writing-to-auth-keys-1631'

See merge request !2004

Squashed commits:
Add authorized_keys_enabled to Application Settings
Ensure default settings are exposed in UI
Without this change, `authorized_keys_enabled` is unchecked when it is nil, even if it should be checked by default.
Add “Speed up SSH operations” documentation
Clarify the reasons for disabling writes
Add "How to go back" section
Tweak copy
Update Application Setting screenshot

1 files changed, 12 insertions, 0 deletions

diff --git a/lib/gitlab/shell.rb b/lib/gitlab/shell.rb
index 564047bbd34..20df19c734d 100644
--- a/lib/gitlab/shell.rb
+++ b/lib/gitlab/shell.rb
@@ -183,6 +183,8 @@ module Gitlab
     #   add_key("key-42", "sha-rsa ...")
     #
     def add_key(key_id, key_content)
+      return unless self.authorized_keys_enabled?
+
       gitlab_shell_fast_execute([gitlab_shell_keys_path,
                                  'add-key', key_id, self.class.strip_key(key_content)])
     end
@@ -192,6 +194,8 @@ module Gitlab
     # Ex.
     #   batch_add_keys { |adder| adder.add_key("key-42", "sha-rsa ...") }
     def batch_add_keys(&block)
+      return unless self.authorized_keys_enabled?
+
       IO.popen(%W(#{gitlab_shell_path}/bin/gitlab-keys batch-add-keys), 'w') do |io|
         yield(KeyAdder.new(io))
       end
@@ -203,6 +207,8 @@ module Gitlab
     #   remove_key("key-342", "sha-rsa ...")
     #
     def remove_key(key_id, key_content)
+      return unless self.authorized_keys_enabled?
+
       args = [gitlab_shell_keys_path, 'rm-key', key_id]
       args << key_content if key_content
 
@@ -215,6 +221,8 @@ module Gitlab
     #   remove_all_keys
     #
     def remove_all_keys
+      return unless self.authorized_keys_enabled?
+
       gitlab_shell_fast_execute([gitlab_shell_keys_path, 'clear'])
     end
 
@@ -410,5 +418,9 @@ module Gitlab
       # need to do the same here...
       raise Error, e
     end
+
+    def authorized_keys_enabled?
+      current_application_settings.authorized_keys_enabled
+    end
   end
 end