Convert authentication generator to Rails command

Generators require the whole app to be booted, which involves having
access to the DB, loading all controlers, etc. which we don't need for
just generating the credentials, and might not work when trying to add
production credentials because many apps aren't prepared to boot for
production in another environment.

README.md

@@ -68,12 +68,12 @@ mission_control:
 If no credentials are configured, Mission Control won't be accessible. To set these up, you can run the generator provided like this:
 
 ```
-bin/rails mission_control:jobs:authentication:init
+bin/rails mission_control:jobs:authentication:configure
 ```
 
 To set them up for different environments you can use the `RAILS_ENV` environment variable, like this:
 ```
-RAILS_ENV=production bin/rails mission_control:jobs:authentication:init
+RAILS_ENV=production bin/rails mission_control:jobs:authentication:configure
 ```
 
 #### Custom authentication

lib/generators/mission_control/jobs/authentication_generator.rb → lib/mission_control/jobs/authentication.rb

@@ -1,5 +1,9 @@
-class MissionControl::Jobs::AuthenticationGenerator < Rails::Generators::Base
-  def init
+class MissionControl::Jobs::Authentication < Rails::Command::Base
+  def self.configure
+    new.configure
+  end
+
+  def configure
     if credentials_accessible?
       if authentication_configured?
         say "HTTP Basic Authentication is already configured for `#{Rails.env}`. You can edit it using `credentials:edit`"
@@ -26,6 +30,8 @@ def init
   end
 
   private
+    attr_reader :environment
+
     def credentials_accessible?
       credentials.read.present?
     end

lib/mission_control/jobs/tasks.rb

@@ -1,8 +1,8 @@
 namespace :mission_control do
   namespace :jobs do
     desc "Configure HTTP Basic Authentication"
-    task "authentication:init" do
-      Rails::Command.invoke :generate, [ "mission_control:jobs:authentication" ]
+    task "authentication:configure" => :environment do
+      MissionControl::Jobs::Authentication.configure
     end
   end
 end