Given an an activation key, look up and activate the user
    account corresponding to that key (if possible).

def activate(request, activation_key=None):
    """
    Given an an activation key, look up and activate the user
    account corresponding to that key (if possible).

    """
    utils.activate_user(activation_key)
    # if not activated
    success_url = utils.get_settings('REGISTRATION_API_ACTIVATION_SUCCESS_URL')
    if success_url is not None:
        return HttpResponseRedirect(success_url)