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from datetime import date
from django.conf import settings
from django.utils.crypto import constant_time_compare, salted_hmac
from django.utils.http import base36_to_int, int_to_base36
class PasswordResetTokenGenerator:
"""
Strategy object used to generate and check tokens for the password
reset mechanism.
"""
key_salt = "django.contrib.auth.tokens.PasswordResetTokenGenerator"
secret = settings.SECRET_KEY
def make_token(self, user):
"""
Return a token that can be used once to do a password reset
for the given user.
"""
return self._make_token_with_timestamp(user, self._num_days(self._today()))
def check_token(self, user, token):
"""
Check that a password reset token is correct for a given user.
"""
if not (user and token):
return False
# Parse the token
try:
ts_b36, hash = token.split("-")
except ValueError:
return False
try:
ts = base36_to_int(ts_b36)
except ValueError:
return False
# Check that the timestamp/uid has not been tampered with
if not constant_time_compare(self._make_token_with_timestamp(user, ts), token):
return False
# Check the timestamp is within limit. Timestamps are rounded to
# midnight (server time) providing a resolution of only 1 day. If a
# link is generated 5 minutes before midnight and used 6 minutes later,
# that counts as 1 day. Therefore, PASSWORD_RESET_TIMEOUT_DAYS = 1 means
# "at least 1 day, could be up to 2."
if (self._num_days(self._today()) - ts) > settings.PASSWORD_RESET_TIMEOUT_DAYS:
return False
return True
def _make_token_with_timestamp(self, user, timestamp):
# timestamp is number of days since 2001-1-1. Converted to
# base 36, this gives us a 3 digit string until about 2121
ts_b36 = int_to_base36(timestamp)
hash = salted_hmac(
self.key_salt,
self._make_hash_value(user, timestamp),
secret=self.secret,
).hexdigest()[::2] # Limit to 20 characters to shorten the URL.
return "%s-%s" % (ts_b36, hash)
def _make_hash_value(self, user, timestamp):
"""
Hash the user's primary key and some user state that's sure to change
after a password reset to produce a token that invalidated when it's
used:
1. The password field will change upon a password reset (even if the
same password is chosen, due to password salting).
2. The last_login field will usually be updated very shortly after
a password reset.
Failing those things, settings.PASSWORD_RESET_TIMEOUT_DAYS eventually
invalidates the token.
Running this data through salted_hmac() prevents password cracking
attempts using the reset token, provided the secret isn't compromised.
"""
# Truncate microseconds so that tokens are consistent even if the
# database doesn't support microseconds.
login_timestamp = '' if user.last_login is None else user.last_login.replace(microsecond=0, tzinfo=None)
return str(user.pk) + user.password + str(login_timestamp) + str(timestamp)
def _num_days(self, dt):
return (dt - date(2001, 1, 1)).days
def _today(self):
# Used for mocking in tests
return date.today()
default_token_generator = PasswordResetTokenGenerator()