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('CSRF protection for aiohttp.web',)

Project description

The library provides csrf (xsrf) protection for aiohttp.web.

https://img.shields.io/travis/wikibusiness/aiohttp-csrf.svg

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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