Get OAuth-two-legged request working in Rails 3.

## application_controller.rb
# Based on work from http://mifsud.me/simple-two-legged-oauth-provider-in-rails-2
# Note that you need a user with :api_key and :secret fields

require 'oauth/request_proxy/rack_request'

class ApplicationController < ActionController::Base
  protect_from_forgery

  protected
  def run_oauth_check
    req = OAuth::RequestProxy::RackRequest.new(request)
    return render :json => { :error => "Invalid request" },
        :status => 400 unless req.parameters['oauth_consumer_key']

    client = User.first :api_key => req.parameters['oauth_consumer_key']
    return render :json => { :error => "Invalid credentials" },
        :status => 401 if client.nil?

    begin
      signature = ::OAuth::Signature.build(::Rack::Request.new(env)) do |rp|
        [nil, client.secret]
      end

      return render :json => { :error => "Invalid credentials" },
          :status => 401 unless signature.verify
    rescue ::OAuth::Signature::UnknownSignatureMethod => e
      return render :json => { :error => "Unknown signature method" }, :status => 400
    end
  end
end