Change the `protect_from_forgery` prepend default to `false`

Per this comment
https://github.com/rails/rails/pull/18334#issuecomment-69234050 we want
`protect_from_forgery` to default to `prepend: false`.

`protect_from_forgery` will now be insterted into the callback chain at the
point it is called in your application. This is useful for cases where you
want to `protect_from_forgery` after you perform required authentication
callbacks or other callbacks that are required to run after forgery protection.

If you want `protect_from_forgery` callbacks to always run first, regardless of
position they are called in your application, then you can add `prepend: true`
to your `protect_from_forgery` call.

Example:

```ruby
protect_from_forgery prepend: true
```

1 files changed, 7 insertions, 7 deletions

diff --git a/actionpack/lib/action_controller/metal/request_forgery_protection.rb b/actionpack/lib/action_controller/metal/request_forgery_protection.rb
index 836ed892dc..26c4550f89 100644
--- a/actionpack/lib/action_controller/metal/request_forgery_protection.rb
+++ b/actionpack/lib/action_controller/metal/request_forgery_protection.rb
@@ -102,13 +102,13 @@ module ActionController #:nodoc:
       #
       # Valid Options:
       #
-      # * <tt>:only/:except</tt> - Only apply forgery protection to a subset of actions. Like <tt>only: [ :create, :create_all ]</tt>.
+      # * <tt>:only/:except</tt> - Only apply forgery protection to a subset of actions. For example <tt>only: [ :create, :create_all ]</tt>.
       # * <tt>:if/:unless</tt> - Turn off the forgery protection entirely depending on the passed Proc or method reference.
-      # * <tt>:prepend</tt> - By default, the verification of the authentication token is added to the front of the
-      #   callback chain. If you need to make the verification depend on other callbacks, like authentication methods
-      #   (say cookies vs OAuth), this might not work for you. Pass <tt>prepend: false</tt> to just add the
-      #   verification callback in the position of the protect_from_forgery call. This means any callbacks added
-      #   before are run first.
+      # * <tt>:prepend</tt> - By default, the verification of the authentication token will be added at the position of the
+      #    protect_from_forgery call in your application. This means any callbacks added before are run first. This is useful
+      #    when you want your forgery protection to depend on other callbacks, like authentication methods (Oauth vs Cookie auth).
+      #
+      #    If you need to add verification to the beginning of the callback chain, use <tt>prepend: true</tt>.
       # * <tt>:with</tt> - Set the method to handle unverified request.
       #
       # Valid unverified request handling methods are:
@@ -116,7 +116,7 @@ module ActionController #:nodoc:
       # * <tt>:reset_session</tt> - Resets the session.
       # * <tt>:null_session</tt> - Provides an empty session during request but doesn't reset it completely. Used as default if <tt>:with</tt> option is not specified.
       def protect_from_forgery(options = {})
-        options = options.reverse_merge(prepend: true)
+        options = options.reverse_merge(prepend: false)
 
         self.forgery_protection_strategy = protection_method_class(options[:with] || :null_session)
         self.request_forgery_protection_token ||= :authenticity_token