Cross-site request forgery (CSRF) protection for aiohttp-server
Project description
aiohttp_csrf
The library provides Cross-server request forgery (csrf/xsrf) protection for aiohttp.web.
This is a fork of https://github.com/bitnom/aiohttp-csrf that adds modern python type annotations, switches to aiohttp AppKey tags, and fixes the historic test suite.
New in Version 1.0.0
- Added type hinting throughout.
- The
aiohttp_csrf.setup()and@csrf_protectdecorators now take separate optional keyword argumentsexception=...anderror_renderer=...to allow customisation of csrf failures. Previously this was an overloaded single argumenterror_renderer. - upgraded dependancy on
blake3,aiohttpandaiohttp-session. - dropped support for Python 3.8
Version in 0.1.0
- uses Blake3 hashes are used by default. This means you must pass
secret_phraseto whichever storage backend is being used to generate tokens, e.g.aiohttp_csrf.storage.SessionStorage
Basic usage
The library allows you to implement csrf (xsrf) protection for requests
Basic usage example:
import aiohttp_csrf
from aiohttp import web
FORM_FIELD_NAME = '_csrf_token'
COOKIE_NAME = 'csrf_token'
def make_app():
csrf_policy = aiohttp_csrf.policy.FormPolicy(FORM_FIELD_NAME)
csrf_storage = aiohttp_csrf.storage.CookieStorage(COOKIE_NAME)
app = web.Application()
aiohttp_csrf.setup(app, policy=csrf_policy, storage=csrf_storage)
app.middlewares.append(aiohttp_csrf.csrf_middleware)
async def handler_get_form_with_token(request):
token = await aiohttp_csrf.generate_token(request)
body = '''
<html>
<head><title>Form with csrf protection</title></head>
<body>
<form method="POST" action="/">
<input type="hidden" name="{field_name}" value="{token}" />
<input type="text" name="name" />
<input type="submit" value="Say hello">
</form>
</body>
</html>
''' # noqa
body = body.format(field_name=FORM_FIELD_NAME, token=token)
return web.Response(
body=body.encode('utf-8'),
content_type='text/html',
)
async def handler_post_check(request):
post = await request.post()
body = 'Hello, {name}'.format(name=post['name'])
return web.Response(
body=body.encode('utf-8'),
content_type='text/html',
)
app.router.add_route(
'GET',
'/',
handler_get_form_with_token,
)
app.router.add_route(
'POST',
'/',
handler_post_check,
)
return app
web.run_app(make_app())
Initialize
First of all, you need to initialize aiohttp_csrf in your application:
app = web.Application()
csrf_policy = aiohttp_csrf.policy.FormPolicy(FORM_FIELD_NAME)
csrf_storage = aiohttp_csrf.storage.CookieStorage(COOKIE_NAME)
aiohttp_csrf.setup(app, policy=csrf_policy, storage=csrf_storage)
Middleware and decorators
After initialize you can use @aiohttp_csrf.csrf_protect for handlers, that you want to protect. Or you can
initialize aiohttp_csrf.csrf_middleware and do not disturb about using
decorator (full middleware example here):
# ...
app.middlewares.append(aiohttp_csrf.csrf_middleware)
# ...
In this case all your handlers will be protected.
Note: we strongly recommend to use aiohttp_csrf.csrf_middleware and @aiohttp_csrf.csrf_exempt instead of
manually managing with @aiohttp_csrf.csrf_protect. But if you prefer to use @aiohttp_csrf.csrf_protect, don't forget
to use @aiohttp_csrf.csrf_protect for both methods: GET and
POST (manual protection example)
If you want to use middleware, but need handlers without protection, you can use @aiohttp_csrf.csrf_exempt. Mark you
handler with this decorator and this handler will not check the token:
@aiohttp_csrf.csrf_exempt
async def handler_post_not_check(request):
...
Generate token
For generate token you need to call aiohttp_csrf.generate_token in your handler:
@aiohttp_csrf.csrf_protect
async def handler_get(request):
token = await aiohttp_csrf.generate_token(request)
...
Advanced usage
Policies
You can use different policies for check tokens. Library provides 3 types of policy:
- FormPolicy. This policy will search token in the body of your POST request (Usually use for forms) or as a GET variable of the same name. You need to specify name of field that will be checked.
- HeaderPolicy. This policy will search token in headers of your POST request (Usually use for AJAX requests). You need to specify name of header that will be checked.
- FormAndHeaderPolicy. This policy combines behavior of FormPolicy and HeaderPolicy.
You can implement your custom policies if needed. But make sure that your custom policy
implements aiohttp_csrf.policy.AbstractPolicy interface.
Storages
You can use different types of storages for storing token. Library provides 2 types of storage:
- CookieStorage. Your token will be stored in cookie variable. You need to specify cookie name.
- SessionStorage. Your token will be stored in session. You need to specify session variable name.
Important: If you want to use session storage, you need setup aiohttp_session in your application (session storage example)
You can implement your custom storages if needed. But make sure that your custom storage
implements aiohttp_csrf.storage.AbstractStorage interface.
Token generators
You can use different token generator in your application. By default storages
using aiohttp_csrf.token_generator.SimpleTokenGenerator
But if you need more secure token generator - you can use aiohttp_csrf.token_generator.HashedTokenGenerator
And you can implement your custom token generators if needed. But make sure that your custom token generator
implements aiohttp_csrf.token_generator.AbstractTokenGenerator interface.
Invalid token behavior
By default, if token is invalid, aiohttp_csrf will raise aiohttp.web.HTTPForbidden exception.
You have ability to specify your custom error handler. It can be:
- callable instance. Input parameter - aiohttp request.
def custom_error_handler(request):
# do something
return aiohttp.web.Response(status=403)
# or
async def custom_async_error_handler(request):
# await do something
return aiohttp.web.Response(status=403)
It will be called instead of protected handler.
- sub class of Exception. In this case this Exception will be raised.
class CustomException(Exception):
pass
You can specify custom error handler globally, when initialize aiohttp_csrf in your application:
...
class CustomException(Exception):
pass
...
aiohttp_csrf.setup(app, policy=csrf_policy, storage=csrf_storage, error_renderer=CustomException)
...
In this case custom error handler will be applied to all protected handlers.
Or you can specify custom error handler locally, for specific handler:
...
class CustomException(Exception):
pass
...
@aiohttp_csrf.csrf_protect(error_renderer=CustomException)
def handler_with_custom_csrf_error(request):
...
In this case custom error handler will be applied to this handler only. For all other handlers will be applied global error handler.
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