Basic authentication on Tornado with a decorator

login.html

        <div id="main-container">
            <div id="main">
                <h1>
                    <img alt="scubabook logo" src="{{ static_url("img/logo.png") }}">
                </h1>
                <div id="login-form">
                    <form action="/auth/login/" method="post" id="login_form">
                        <fieldset>
                            <label for="username">Username</label>
                            <input autocapitalize="off" autocorrect="off" class="text-input" id="username" name="username" tabindex="1" type="text" value="">
                        </fieldset>

                        <fieldset>
                            <label for="password">Password</label>
                            <input class="text-input" id="password" name="password" tabindex="2" type="password" value="">
                        </fieldset>
                        <fieldset>
                            <span class="errormessage">{{errormessage}}</span>
                        </fieldset>

                        <div id="form_btn">
                            <input id="signin-btn" class="btn btn-blue" type="submit" value="Sign In" tabindex="3">
                            <!-- <a href="/sb/"><input id="inscription-btn" class="btn btn-red" value="Inscription" tabindex="3"></a> -->
                        </div>
                    </form>
                </div>
            </div>
        </div>

settings.py

import os
DEBUG = True
DIRNAME = os.path.dirname(__file__)
STATIC_PATH = os.path.join(DIRNAME, 'static')
TEMPLATE_PATH = os.path.join(DIRNAME, 'template')

import logging
import sys
#log linked to the standard error stream
logging.basicConfig(level=logging.DEBUG,
                    format='%(asctime)s - %(levelname)-8s - %(message)s',
                    datefmt='%d/%m/%Y %Hh%Mm%Ss')
console = logging.StreamHandler(sys.stderr)

#import base64
#import uuid
#base64.b64encode(uuid.uuid4().bytes + uuid.uuid4().bytes)
COOKIE_SECRET = 'L8LwECiNRxq2N0N2eGxx9MZlrpmuMEimlydNX/vt1LM='

webserver.py

import tornado.auth
import tornado.escape
import tornado.httpserver
import tornado.ioloop
import tornado.options
import tornado.web
import Settings

from tornado.options import define, options

define("port", default=8888, help="run on the given port", type=int)

class BaseHandler(tornado.web.RequestHandler):
    def get_current_user(self):
        return self.get_secure_cookie("user")

class MainHandler(BaseHandler):
    @tornado.web.authenticated
    def get(self):
        username = tornado.escape.xhtml_escape(self.current_user)
        self.write("index.html", username = username)

class AuthLoginHandler(BaseHandler):
    def get(self):
        try:
            errormessage = self.get_argument("error")
        except:
            errormessage = ""
        self.render("login.html", errormessage = errormessage)

    def check_permission(self, password, username):
        if username == "admin" and password == "admin":
            return True
        return False

    def post(self):
        username = self.get_argument("username", "")
        password = self.get_argument("password", "")
        auth = self.check_permission(password, username)
        if auth:
            self.set_current_user(username)
            self.redirect(self.get_argument("next", u"/"))
        else:
            error_msg = u"?error=" + tornado.escape.url_escape("Login incorrect")
            self.redirect(u"/auth/login/" + error_msg)

    def set_current_user(self, user):
        if user:
            self.set_secure_cookie("user", tornado.escape.json_encode(user))
        else:
            self.clear_cookie("user")

class AuthLogoutHandler(BaseHandler):
    def get(self):
        self.clear_cookie("user")
        self.redirect(self.get_argument("next", "/"))

class Application(tornado.web.Application):
    def __init__(self):
        handlers = [
            (r"/", MainHandler),
            (r"/auth/login/", AuthLoginHandler),
            (r"/auth/logout/", AuthLogoutHandler),
        ]
        settings = {
            "template_path":Settings.TEMPLATE_PATH,
            "static_path":Settings.STATIC_PATH,
            "debug":Settings.DEBUG,
            "cookie_secret": Settings.COOKIE_SECRET,
            "login_url": "/auth/login/"
        }
        tornado.web.Application.__init__(self, handlers, **settings)

def main():
    tornado.options.parse_command_line()
    http_server = tornado.httpserver.HTTPServer(Application())
    http_server.listen(options.port)
    tornado.ioloop.IOLoop.instance().start()

if __name__ == "__main__":
    main()

Cheers for gist. to corrected above as follows:

1. set params in the AuthLoginHandler GET call to include nextpage ('/' fallback). passed to template

def get(self):
        params = {
            "errormessage": self.get_argument("error",''),
            "nextpage": self.get_argument("next", "/")
        }
        self.render('login.html', **params)

2. Updated the template to pass on "next" param

<form action="/auth/login?next={{nextpage}}" method="post" id="login_form">

Seems a relatively clean way of fixing

What's the Settings you are importing?