Replace setting custom CORS headers with rack-cors, set it on /oauth/token endpoint

Gemfile

@@ -4,7 +4,6 @@ gem 'rails', '5.0.0.1'
 gem 'sass-rails', '~> 5.0'
 gem 'uglifier', '>= 1.3.0'
 gem 'coffee-rails', '~> 4.1.0'
-gem 'therubyracer', platforms: :ruby
 gem 'jquery-rails'
 gem 'jbuilder', '~> 2.0'
 gem 'sdoc', '~> 0.4.0', group: :doc
@@ -39,6 +38,7 @@ gem 'htmlentities'
 gem 'simple_form'
 gem 'will_paginate'
 gem 'rack-attack'
+gem 'rack-cors', require: 'rack/cors'
 gem 'sidekiq'
 gem 'ledermann-rails-settings'
 gem 'neography'

Gemfile.lock

@@ -157,7 +157,6 @@ GEM
       activerecord (>= 3.1)
     letter_opener (1.4.1)
       launchy (~> 2.2)
-    libv8 (3.16.14.15)
     link_header (0.0.8)
     lograge (0.4.1)
       actionpack (>= 4, < 5.1)
@@ -219,6 +218,7 @@ GEM
     rack (2.0.1)
     rack-attack (5.0.1)
       rack
+    rack-cors (0.4.0)
     rack-protection (1.5.3)
       rack
     rack-test (0.6.3)
@@ -281,7 +281,6 @@ GEM
       redis-store (~> 1.2.0)
     redis-store (1.2.0)
       redis (>= 2.2)
-    ref (2.0.0)
     responders (2.3.0)
       railties (>= 4.2.0, < 5.1)
     rspec (3.5.0)
@@ -349,9 +348,6 @@ GEM
       activesupport (>= 4.0)
       sprockets (>= 3.0.0)
     temple (0.7.7)
-    therubyracer (0.12.2)
-      libv8 (~> 3.16.14.0)
-      ref
     thor (0.19.1)
     thread_safe (0.3.5)
     tilt (2.0.5)
@@ -419,6 +415,7 @@ DEPENDENCIES
   puma
   rabl
   rack-attack
+  rack-cors
   rails (= 5.0.0.1)
   rails_12factor
   rails_autolink
@@ -433,7 +430,6 @@ DEPENDENCIES
   sidekiq
   simple_form
   simplecov
-  therubyracer
   uglifier (>= 1.3.0)
   webmock
   will_paginate

app/controllers/api_controller.rb

@@ -7,7 +7,6 @@ class ApiController < ApplicationController
   skip_before_action :verify_authenticity_token
 
   before_action :set_rate_limit_headers
-  before_action :set_cors_headers
 
   rescue_from ActiveRecord::RecordInvalid do |e|
     render json: { error: e.to_s }, status: 422
@@ -50,13 +49,6 @@ class ApiController < ApplicationController
     response.headers['X-RateLimit-Reset']     = (now + (match_data[:period] - now.to_i % match_data[:period])).to_s
   end
 
-  def set_cors_headers
-    response.headers['Access-Control-Allow-Origin']   = '*'
-    response.headers['Access-Control-Allow-Methods']  = 'POST, PUT, DELETE, GET, OPTIONS'
-    response.headers['Access-Control-Request-Method'] = '*'
-    response.headers['Access-Control-Allow-Headers']  = 'Origin, X-Requested-With, Content-Type, Accept, Authorization'
-  end
-
   def set_pagination_headers(next_path = nil, prev_path = nil)
     links = []
     links << [next_path, [['rel', 'next']]] if next_path

config/application.rb

@@ -27,6 +27,15 @@ module Mastodon
 
     config.active_job.queue_adapter = :sidekiq
 
+    config.middleware.insert_before 0, Rack::Cors do
+      allow do
+        origins  '*'
+
+        resource '/api/*',       :headers => :any, :methods => [:post, :put, :delete, :get, :options], credentials: false
+        resource '/oauth/token', :headers => :any, :methods => [:post], credentials: false
+      end
+    end
+
     config.middleware.use Rack::Attack
     config.middleware.use Rack::Deflater