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- """
- A provided CSRF implementation which puts CSRF data in a session.
- This can be used fairly comfortably with many `request.session` type
- objects, including the Werkzeug/Flask session store, Django sessions, and
- potentially other similar objects which use a dict-like API for storing
- session keys.
- The basic concept is a randomly generated value is stored in the user's
- session, and an hmac-sha1 of it (along with an optional expiration time,
- for extra security) is used as the value of the csrf_token. If this token
- validates with the hmac of the random value + expiration time, and the
- expiration time is not passed, the CSRF validation will pass.
- """
- from __future__ import unicode_literals
- import hmac
- import os
- from hashlib import sha1
- from datetime import datetime, timedelta
- from ...validators import ValidationError
- from .form import SecureForm
- __all__ = ('SessionSecureForm', )
- class SessionSecureForm(SecureForm):
- TIME_FORMAT = '%Y%m%d%H%M%S'
- TIME_LIMIT = timedelta(minutes=30)
- SECRET_KEY = None
- def generate_csrf_token(self, csrf_context):
- if self.SECRET_KEY is None:
- raise Exception('must set SECRET_KEY in a subclass of this form for it to work')
- if csrf_context is None:
- raise TypeError('Must provide a session-like object as csrf context')
- session = getattr(csrf_context, 'session', csrf_context)
- if 'csrf' not in session:
- session['csrf'] = sha1(os.urandom(64)).hexdigest()
- self.csrf_token.csrf_key = session['csrf']
- if self.TIME_LIMIT:
- expires = (datetime.now() + self.TIME_LIMIT).strftime(self.TIME_FORMAT)
- csrf_build = '%s%s' % (session['csrf'], expires)
- else:
- expires = ''
- csrf_build = session['csrf']
- hmac_csrf = hmac.new(self.SECRET_KEY, csrf_build.encode('utf8'), digestmod=sha1)
- return '%s##%s' % (expires, hmac_csrf.hexdigest())
- def validate_csrf_token(self, field):
- if not field.data or '##' not in field.data:
- raise ValidationError(field.gettext('CSRF token missing'))
- expires, hmac_csrf = field.data.split('##')
- check_val = (field.csrf_key + expires).encode('utf8')
- hmac_compare = hmac.new(self.SECRET_KEY, check_val, digestmod=sha1)
- if hmac_compare.hexdigest() != hmac_csrf:
- raise ValidationError(field.gettext('CSRF failed'))
- if self.TIME_LIMIT:
- now_formatted = datetime.now().strftime(self.TIME_FORMAT)
- if now_formatted > expires:
- raise ValidationError(field.gettext('CSRF token expired'))
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