Rails Responds with 404 on CORS Preflight Options Request

Here’s a solution with the rack-cors gem, which you said you tried. As others have mentioned, you didn’t give much detail in regards to which front-end framework you’re using and what the actual request looks like. So the following may not apply to you, but I hope it helps someone.

In my case, the gem worked fine until I used PUT (or PATCH or DELETE).

If you look in your browser developer console, look at the request headers, and you should have a line like this:

Access-Control-Request-Method: PUT

The important thing to note is that the methods you pass to resource are for the Access-Control-Request-Method, not the Request Method that is to come after the pre-flight check.

Note how I have :methods => [:get, :post, :options, :delete, :put, :patch] that will include all the methods I care about.

Thus your entire config section should look something like this, for development.rb:

# This handles cross-origin resource sharing.
# See: https://github.com/cyu/rack-cors
config.middleware.insert_before 0, "Rack::Cors" do
  allow do
    # In development, we don't care about the origin.
    origins '*'
    # Reminder: On the following line, the 'methods' refer to the 'Access-
    # Control-Request-Method', not the normal Request Method.
    resource '*', :headers => :any, :methods => [:get, :post, :options, :delete, :put, :patch], credentials: true

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