var login_user = function (login_url) {

  /* Function that handles the post login request changes. */

  var process_login_response = function (raw_data) {

    /* We expect an exception when login fails. Read comment with catch. */

    try {

      data = $.parseJSON(raw_data);

      if (data.authentication == "success") {

        /* Login succeeded */

        if (data.markup) {

          /* Replace the HTML with the user actions since

           * the request came from a URL other than logout page */

          $("div#useraction").replaceWith(data.markup);

        } else if (data.redirect) {

          /* Reload the page to the pytask home page since

           * the login request came from logout page. This

           * is done because the logout text says you have

           * been logged out, which will be awkward after

           * user re-logs in. */

          window.location.href=data.redirect;

        }

      }

    } catch (e) {

      /* Login failed so the login view returned to the same view as

       * the existing page from which the call was made and thus we

       * get html. So let us display the error. */

      $('div #loginform #error').show();

    }

  }

  /* Attach a handler which does the form post upon the submit

   * button is pressed on the login form. */

  $(document).ready(function () {

    $('#form_login').submit(function() {

      $.post(

        login_url,

        $("#form_login").serialize(),

        process_login_response);

      return false;

    });

  });

}