Source code
from datetime import datetime
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"
algorithm = None
_secret = None
_secret_fallbacks = None
def __init__(self):
self.algorithm = self.algorithm or "sha256"
def _get_secret(self):
return self._secret or settings.SECRET_KEY
def _set_secret(self, secret):
self._secret = secret
secret = property(_get_secret, _set_secret)
def _get_fallbacks(self):
if self._secret_fallbacks is None:
return settings.SECRET_KEY_FALLBACKS
return self._secret_fallbacks
def _set_fallbacks(self, fallbacks):
self._secret_fallbacks = fallbacks
secret_fallbacks = property(_get_fallbacks, _set_fallbacks)
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_seconds(self._now()),
self.secret,
)
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, _ = 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
for secret in [self.secret, *self.secret_fallbacks]:
if constant_time_compare(
self._make_token_with_timestamp(user, ts, secret),
token,
):
break
else:
return False
# Check the timestamp is within limit.
if (self._num_seconds(self._now()) - ts) > settings.PASSWORD_RESET_TIMEOUT:
return False
return True
def _make_token_with_timestamp(self, user, timestamp, secret):
# timestamp is number of seconds since 2001-1-1. Converted to base 36,
# this gives us a 6 digit string until about 2069.
ts_b36 = int_to_base36(timestamp)
hash_string = salted_hmac(
self.key_salt,
self._make_hash_value(user, timestamp),
secret=secret,
algorithm=self.algorithm,
).hexdigest()[
::2
] # Limit to shorten the URL.
return "%s-%s" % (ts_b36, hash_string)
def _make_hash_value(self, user, timestamp):
"""
Hash the user's primary key, email (if available), and some user state
that's sure to change after a password reset to produce a token that is
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 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)
)
email_field = user.get_email_field_name()
email = getattr(user, email_field, "") or ""
return f"{user.pk}{user.password}{login_timestamp}{timestamp}{email}"
def _num_seconds(self, dt):
return int((dt - datetime(2001, 1, 1)).total_seconds())
def _now(self):
# Used for mocking in tests
return datetime.now()