CherryPy Custom Tool for user authentication

Question

I'm trying to set up a simple way of decorating methods in my CherryPy controller classes so that a user is redirected to the login page if they haven't authenticated yet. I was going to do a basic Python decorator, but an answer here suggested I use a CherryPy Custom Tool instead. So I'm trying to do that, but I can't get it to work. Here's what I have:

def authenticate():
    user = cherrypy.session.get('user', None)
    if not user:
        raise cherrypy.HTTPRedirect('/?errMsg=Please%20log%20in%20first')

cherrypy.tools.authenticate = cherrypy.Tool('on_start_resource', authenticate)

The /home page is a page that should be restricted to authenticated users, so I have this:

@cherrypy.expose
@cherrypy.tools.authenticate
def home(self, **kwargs):
    tmpl = TemplateDir.get_template('home.mako')
    return tmpl.render()

However, I get this error when I try to start my web site:

Traceback (most recent call last):
  File ".\example.py", line 3, in <module>
    from controller.main import Root
  File "C:\...\controller\main.py", line 9, in <module>
    class Root(BaseModule):
  File "C:\...\controller\main.py", line 19, in Root
    @cherrypy.tools.authenticate
  File "C:\Python26\lib\site-packages\cherrypy\_cptools.py", line 119, in
   __call__ % self._name)
TypeError: The 'authenticate' Tool does not accept positional arguments; you must
  use keyword arguments.

Edit: okay, if I change my use of the custom tool to have parentheses, I get a different error.

@cherrypy.expose
@cherrypy.tools.authenticate() # Magic parentheses...
def home(self, **kwargs):
    ...

Now I get:

Traceback (most recent call last):
  File "C:\Python26\lib\site-packages\cherrypy\_cprequest.py", line 625, in respond
    self.hooks.run('on_start_resource')
  File "C:\Python26\lib\site-packages\cherrypy\_cprequest.py", line 97, in run
    hook()
  File "C:\Python26\lib\site-packages\cherrypy\_cprequest.py", line 57, in __call__
    return self.callback(**self.kwargs)
  File ".\example.py", line 40, in authenticate
    user = cherrypy.session.get('user', None)
AttributeError: 'module' object has no attribute 'session'

Edit: I have sessions turned on:

cherrypy.tools.sessions.storage_type = 'file'
cherrypy.tools.sessions.storage_path = r'%s\sessions' % curDir
cherrypy.tools.sessions.timeout = 60
cherrypy.tree.mount(Root(), "/", config={
    '/static': {
        'tools.staticdir.on':True,
        'tools.staticdir.dir':r'%s\static' % curDir,
    },
    '/': {
        'tools.sessions.on':True,
    }
})

When I first load the page with my custom tool decorator on the web method, I get this error:

AttributeError: 'module' object has no attribute 'session'

Then when I reload the page, I get this error:

AttributeError: '_Serving' object has no attribute 'session'

Edit: even trying this much in my controller class, I still get the 'module object has no attribute session' error:

class Root(BaseModule):
    _cp_config = {'tools.sessions.on': True}
    sess = cherrypy.session # Error here
    ...

Answer 1

I was using the wrong hook. Changing:

cherrypy.tools.authenticate = cherrypy.Tool('on_start_resource', authenticate)

To:

cherrypy.tools.authenticate = cherrypy.Tool('before_handler', authenticate)

Fixed the problem. Apparently my authenticate method was getting called before sessions had been turned on, so it couldn't access cherrypy.session. I didn't need any session-turn-on stuff in my controllers; all that was necessary was the following in my server-start script:

def authenticate():
    ...
cherrypy.tools.authenticate = cherrypy.Tool('before_handler', authenticate)
cherrypy.tree.mount(Root(), "/", config={
    "/": {
        'tools.sessions.on':True,
        'tools.sessions.storage_type':'file',
        'tools.sessions.storage_path':r'%s\sessions' % curDir,
        'tools.sessions.timeout':60
    }, ...
})

Then, in my controller on a restricted method:

@cherrypy.expose
@cherrypy.tools.authenticate()
def home(self, **kwargs):
    ...