origin-relative-ref = path-absolute [ "?" query ] [ "#" fragment ]

        with the exception that '%' escapes are not validated and '#' is

        allowed inside the fragment part.

        """

        return _re.match(came_from) is not None

    def index(self):

        c.came_from = request.GET.get('came_from', '')

        if c.came_from:

            if not self._validate_came_from(c.came_from):

                log.error('Invalid came_from (not server-relative): %r', c.came_from)

                raise HTTPBadRequest()

        else:

            c.came_from = url('home')

        if request.POST:

            # import Login Form validator class

            login_form = LoginForm()()

            try:

                c.form_result = login_form.to_python(dict(request.POST))

                # form checks for username/password, now we're authenticated

                username = c.form_result['username']

                assert user is not None  # the same user get just passed in the form validation

            except formencode.Invalid as errors:

                defaults = errors.value

                # remove password from filling in form again

                defaults.pop('password', None)

                return htmlfill.render(

                    render('/login.html'),

                    defaults=errors.value,

                    errors=errors.error_dict or {},

                    prefix_error=False,

                    encoding="UTF-8",

                    force_defaults=False)

            except UserCreationError as e:

                # container auth or other auth functions that create users on

                # the fly can throw this exception signaling that there's issue

                # with user creation, explanation should be provided in

                # Exception itself

                h.flash(e, 'error')

            else:

                auth_user = log_in_user(user, c.form_result['remember'], is_external_auth=False, ip_addr=request.ip_addr)

                if auth_user:

                    raise HTTPFound(location=c.came_from)

                h.flash(_('Authentication failed.'), 'error')

        else:

            log.debug('User is empty not allowed to authenticate')

            return False

        if user and user.extern_type and user.extern_type != plugin_name:

            log.debug('User %s should authenticate using %s this is %s, skipping',

                      user, user.extern_type, plugin_name)

            return False

        return True

    def get_user(self, username=None, **kwargs):

        """

        Helper method for user fetching in plugins, by default it's using

        simple fetch by username, but this method can be customized in plugins

        eg. container auth plugin to fetch user by environ params

        :param username: username if given to fetch from database

        :param kwargs: extra arguments needed for user fetching.

        """

        user = None

        log.debug('Trying to fetch user `%s` from Kallithea database',

                  username)

        if username:

            user = User.get_by_username_or_email(username)

        else:

            log.debug('provided username:`%s` is empty skipping...', username)

        return user

    def settings(self):

        """

        Return a list of the form:

        [

            {

                "name": "OPTION_NAME",

                "type": "[bool|password|string|int|select]",

                ["values": ["opt1", "opt2", ...]]

                "validator": "expr"

                "description": "A short description of the option" [,

                "default": Default Value],

                ["formname": "Friendly Name for Forms"]

            } [, ...]

        ]

        This is used to interrogate the authentication plugin as to what

        settings it expects to be present and configured.

        'type' is a shorthand notation for what kind of value this option is.

        This is primarily used by the auth web form to control how the option

        try:

            self._user_data = ascii_bytes(ext_json.dumps(val))

        except Exception:

            log.error(traceback.format_exc())

    def __repr__(self):

        return "<%s %s: %r')>" % (self.__class__.__name__, self.user_id, self.username)

    @classmethod

    def guess_instance(cls, value):

        return super(User, cls).guess_instance(value, User.get_by_username)

    @classmethod

    def get_or_404(cls, id_, allow_default=True):

        '''

        Overridden version of BaseDbModel.get_or_404, with an extra check on

        the default user.

        '''

        user = super(User, cls).get_or_404(id_)

        if not allow_default and user.is_default_user:

            raise DefaultUserException()

        return user

    @classmethod

        """

        For anything that looks like an email address, look up by the email address (matching

        case insensitively).

        For anything else, try to look up by the user name.

        This assumes no normal username can have '@' symbol.

        """

        if '@' in username_or_email:

            return User.get_by_email(username_or_email, cache=cache)

        else:

            return User.get_by_username(username_or_email, case_insensitive=case_insensitive, cache=cache)

    @classmethod

    def get_by_username(cls, username, case_insensitive=False, cache=False):

        if case_insensitive:

            q = cls.query().filter(sqlalchemy.func.lower(cls.username) == sqlalchemy.func.lower(username))

        else:

            q = cls.query().filter(cls.username == username)

        if cache:

            q = q.options(FromCache(

                            "sql_cache_short",

                            "get_user_%s" % _hash_key(username)

                          )