Add support for OmniAuth callbacks defined at runtime

runtime_callback.rb

#
# Including this module in an OmniAuth strategy implementation allows it to have
# a runtime-defined callback path extension. The callback path always begins
# with the predefined callback path, but may extend it. Specify a callback path
# extension at runtime by passing the 'callback' parameter to the request-phase
# auth URL. For example, the below URL:
#
#     http://your.host/auth/facebook?callback=users/create
#
# Will issue a callback to:
#
#     http://your.host/auth/facebook/callback/users/create
#
# You should thus configure your routes file to send this route to the
# appropriate controller/action.
#
module OmniAuth
  module RuntimeCallback
    def call!(env)
      @env = env
      if callback_url_prefix =~ request.path
        callback_phase
      else
        super
      end
    end

    def callback_url
      if callback_url_prefix =~ request.path
        "#{request.scheme}://#{request.host_with_port}#{request.path}"
      elsif request.params.has_key?('callback')
        callback = request.params['callback']
        if callback =~ %r(^/)
          "#{super}#{callback}"
        else
          "#{super}/#{callback}"
        end
      else
        super
      end
    end

    private

    def callback_url_prefix
      %r(^#{Regexp.escape(OmniAuth.config.path_prefix)}/#{name}/callback/)
    end
  end
end

runtime_options.rb

module OmniAuth
  #
  # Include this module in a strategy to pass request parameters in the request
  # phase through to the auth request.
  #
  module RuntimeOptions
    def call!(env)
      @env = env
      request.params.each_pair do |key, value|
        options[key.to_sym] = value if key != 'callback'
      end
      super
    end
  end
end