facebook.js

var connect: function () {
  FB.Connect.showPermissionDialog("email", function () {
    $.ajax({
      url: '/user_session',
      type: 'POST',
      dataType: 'json',
      data: {facebook_connecting: 1},
      success: function (data) {
        // reload page... etc.
      }
    });
  });
};

user_session.rb

class UserSession < Authlogic::Session::Base

  # ...

  facebook_auth_if      :facebook_connecting

  private

  # Override AuthlogicFacebookConnect::Session#authenticating_with...? because
  # it hijacks the login from other methods (email/pass and Twitter). We need
  # to check if the param :facebook_connecting is being passed as well, which
  # can be found in facebook.js.
  def facebook_connecting
    controller.params[:facebook_connecting].present?
  end

  # ...

end