repoze.what – Authorization in TurboGears 2 applications¶| Status: | Official |
|---|---|
| Website: | http://static.repoze.org/whatdocs/ |
Overview
This document describes how repoze.what is integrated into TurboGears
and how you may get started with it. For more information, you may want
to check repoze.what’s website.
repoze.what is a highly extensible and fully documented authorization
framework which is well integrated into TurboGears (in fact, it started as a TG
subproject).
If you enabled authentication and authorization in your project when it was generated by TurboGears, then it’s been set up to store your users, groups and permissions in SQLAlchemy-managed tables.
Your users’ table is used by repoze.who to authenticate them and also
by repoze.what (along with the groups table) to find the groups to which
the user belongs. Then your permissions table is only used by
repoze.what to find the permissions granted to the groups to which the
current user belongs.
This is all configured through repoze.what and you are free to replace
these settings whenever you want. If you want to keep the three tables above
but you need more flexibility, you will get it by adjusting your
{yourproject}.config.app_cfg module accordingly. If you don’t want to keep
the three tables above for authentication or authorization (e.g., you want to
use OpenID authentication and store your groups and permissions in XML
files), then you should check the repoze.what manual to learn how
to configure your TG application. (See also Adding OpenID Support which describes
the process of setting up OpenID authentication in detail).
You can even get rid of authorization based on groups and permissions and use
other authorization patterns (e.g., roles, based on network components) or
simply use a mix of patterns – if so, check the repoze.what
manual to learn more.
repoze.what.predicates¶repoze.what allows you to define access rules based on so-called
“predicate checkers”.
A predicate is the condition that must be met for the user to be able to
access the requested source. Such a predicate, or condition, may be made
up of more predicates – those are called compound predicates. Action
controllers, or controllers, may have only one predicate, be it single or
compound.
A predicate checker is a class that checks whether a predicate or
condition is met.
If a user is not logged in, or does not have the proper permissions, the
predicate checker throws a 401 (HTTP Unauthorized) which is caught by the
repoze.who middleware to display the login page allowing
the user to login, and redirecting the user back to the proper page when they
are done.
For example, if you have a predicate which is “grant access to any authenticated user”, then you can use the following built-in predicate checker:
from repoze.what.predicates import not_anonymous
p = not_anonymous(msg='Only logged in users can read this post')
Or if you have a predicate which is “allow access to root or anyone with the ‘manage’ permission”, then you may use the following built-in predicate checker:
from repoze.what.predicates import Any, is_user, has_permission
p = Any(is_user('root'), has_permission('manage'),
msg='Only administrators can remove blog posts')
As you may have noticed, predicates receive the msg keyword argument to
use its value as the error message if the predicate is not met. It’s optional
and if you don’t define it, the built-in predicates will use the default
English message; you may take advantage of this functionality to make such
messages translatable.
Note
Good predicate messages don’t explain what went wrong; instead, they describe the predicate in the current context (regardless of whether the condition is met or not!). This is because such messages may be used in places other than in a user-visible message (e.g., in the log file).
Below are described the convenient utilities TurboGears provides to deal with predicates in your applications.
You can control access on a per action basis by using the
tg.decorators.require() decorator on the actions in question. All you have
to do is pass the predicate to that decorator. For example:
# ...
from tg import require
from repoze.what.predicates import Any, is_user, has_permission
# ...
class MyCoolController(BaseController):
# ...
@expose('yourproject.templates.start_vacations')
@require(Any(is_user('root'), has_permission('manage'),
msg='Only administrators can remove blog posts'))
def only_for_admins():
flash('Hello admin!')
dict()
# ...
If you want that all the actions from a given controller meet a common
authorization criteria, then you may define the allow_only attribute of
your controller class:
from yourproject.lib.base import BaseController
class Admin(BaseController):
allow_only = authorize.has_permission('manage')
@expose('yourproject.templates.index')
def index(self):
flash(_("Secure controller here"))
return dict(page='index')
@expose('yourproject.templates.index')
def some_where(self):
"""This is protected too.
Only those with "manage" permissions may access.
"""
return dict()
Warning
Do not use this feature if the login URL would be mapped to that controller, as that would result in a cyclic redirect.
These are the predicate checkers that are included with repoze.what,
although the list below may not always be up-to-date:
repoze.what.predicates.not_anonymous¶Check that the current user has been authenticated.
repoze.what.predicates.is_user(user_name)¶Check that the authenticated user’s user name is the specified one.
| Parameters: | user_name (str) – The required user name. |
|---|
repoze.what.predicates.in_group(group_name)¶Check that the user belongs to the specified group.
| Parameters: | group_name (str) – The name of the group to which the user must belong. |
|---|
repoze.what.predicates.in_all_groups(group1_name, group2_name[, group3_name ...])¶Check that the user belongs to all of the specified groups.
| Parameters: |
|
|---|
repoze.what.predicates.in_any_group(group1_name[, group2_name ...])¶Check that the user belongs to at least one of the specified groups.
| Parameters: |
|
|---|
repoze.what.predicates.has_permission(permission_name)¶Check that the current user has the specified permission.
| Parameters: | permission_name – The name of the permission that must be granted to the user. |
|---|
repoze.what.predicates.has_all_permissions(permission1_name, permission2_name[, permission3_name...])¶Check that the current user has been granted all of the specified permissions.
| Parameters: |
|
|---|
repoze.what.predicates.has_any_permission(permission1_name[, permission2_name ...])¶Check that the user has at least one of the specified permissions.
| Parameters: |
|
|---|
repoze.what.predicates.Not(predicate)¶Negate the specified predicate.
| Parameters: | predicate – The predicate to be negated. |
|---|
You may create your own predicate checkers if the built-in ones are not enough to achieve a given task.
To do so, you should extend the repoze.what.predicate.Predicate
class. For example, if your predicate is “Check that the current month is the
specified one”, your predicate checker may look like this:
from datetime import date
from repoze.what.predicates import Predicate
class is_month(Predicate):
message = 'The current month must be %(right_month)s'
def __init__(self, right_month, **kwargs):
self.right_month = right_month
super(is_month, self).__init__(**kwargs)
def evaluate(self, environ, credentials):
if date.today().month != self.right_month:
self.unmet()
Warning
When you create a predicate, don’t try to guess/assume the context in which the predicate is evaluated when you write the predicate message because such a predicate may be used in a different context.
If you defined that class in, say, {yourproject}.lib.auth, you may use it
as in this example:
# ...
from spain_travels.lib.auth import is_month
# ...
class SummerVacations(BaseController):
# ...
@expose('spain_travels.templates.start_vacations')
@authorize.require(is_month(7))
def start_vacations():
flash('Have fun!')
dict()
# ...
You may create a compound predicate by aggregating single (or even compound) predicate checkers with the functions below:
repoze.what.predicates.All(predicate1, predicate2[, predicate3 ...])¶Check that all of the specified predicates are met.
| Parameters: |
|
|---|
repoze.what.predicates.Any(predicate1[, predicate2 ...])¶Check that at least one of the specified predicates is met.
| Parameters: |
|
|---|
But you can also nest compound predicates:
# ...
from yourproject.lib.auth import is_month
# ...
@authorize.require(authorize.All(
Any(is_month(4), is_month(10)),
authorize.has_permission('release')
))
def release_ubuntu(self, **kwargs):
return dict()
# ...
Which translates as “Anyone granted the ‘release’ permission may release a version of Ubuntu, if and only if it’s April or October”.
repoze.what internally¶Note
TurboGears will configure repoze.what for you, if and only if you
have enabled authentication and authorization in
{yourproject}.config.app_cfg.
TurboGears will take your auth settings defined in
{yourproject}.config.app_cfg and then it will configure repoze.what
with such settings using its SQL plugin.
Also, it provides you will the functionality described above:
The @require decorator and the ability to define controller-wide predicates.
That’s it – TurboGears doesn’t deal with repoze.what in any other way,
so it’s absolutely safe for you to stop TurboGears from configuring
repoze.what with its SQL plugin so that you can set it up on your own,
while still using the @require decorator and the ability to control access
at the controller level.