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114 lines
3.3 KiB
Python
114 lines
3.3 KiB
Python
#!/usr/bin/python2.5
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#
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# Copyright 2010 the Melange authors.
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#
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# Licensed under the Apache License, Version 2.0 (the "License");
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# you may not use this file except in compliance with the License.
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# You may obtain a copy of the License at
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#
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# http://www.apache.org/licenses/LICENSE-2.0
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#
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# Unless required by applicable law or agreed to in writing, software
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# distributed under the License is distributed on an "AS IS" BASIS,
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# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
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# See the License for the specific language governing permissions and
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# limitations under the License.
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"""Helper methods for creating & verifying XSRF tokens."""
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__authors__ = [
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'"Doug Coker" <dcoker@google.com>',
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'"Joe Gregorio" <jcgregorio@google.com>',
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]
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import base64
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import hmac
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import os # for urandom
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import time
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from oauth2client import util
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# Delimiter character
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DELIMITER = ':'
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# 1 hour in seconds
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DEFAULT_TIMEOUT_SECS = 1*60*60
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@util.positional(2)
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def generate_token(key, user_id, action_id="", when=None):
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"""Generates a URL-safe token for the given user, action, time tuple.
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Args:
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key: secret key to use.
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user_id: the user ID of the authenticated user.
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action_id: a string identifier of the action they requested
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authorization for.
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when: the time in seconds since the epoch at which the user was
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authorized for this action. If not set the current time is used.
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Returns:
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A string XSRF protection token.
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"""
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when = when or int(time.time())
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digester = hmac.new(key)
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digester.update(str(user_id))
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digester.update(DELIMITER)
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digester.update(action_id)
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digester.update(DELIMITER)
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digester.update(str(when))
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digest = digester.digest()
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token = base64.urlsafe_b64encode('%s%s%d' % (digest,
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DELIMITER,
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when))
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return token
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@util.positional(3)
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def validate_token(key, token, user_id, action_id="", current_time=None):
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"""Validates that the given token authorizes the user for the action.
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Tokens are invalid if the time of issue is too old or if the token
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does not match what generateToken outputs (i.e. the token was forged).
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Args:
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key: secret key to use.
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token: a string of the token generated by generateToken.
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user_id: the user ID of the authenticated user.
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action_id: a string identifier of the action they requested
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authorization for.
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Returns:
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A boolean - True if the user is authorized for the action, False
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otherwise.
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"""
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if not token:
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return False
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try:
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decoded = base64.urlsafe_b64decode(str(token))
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token_time = long(decoded.split(DELIMITER)[-1])
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except (TypeError, ValueError):
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return False
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if current_time is None:
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current_time = time.time()
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# If the token is too old it's not valid.
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if current_time - token_time > DEFAULT_TIMEOUT_SECS:
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return False
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# The given token should match the generated one with the same time.
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expected_token = generate_token(key, user_id, action_id=action_id,
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when=token_time)
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if len(token) != len(expected_token):
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return False
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# Perform constant time comparison to avoid timing attacks
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different = 0
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for x, y in zip(token, expected_token):
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different |= ord(x) ^ ord(y)
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if different:
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return False
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return True
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