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| 1 # | |
| 2 # Copyright 2014 the Melange authors. | |
| 3 # | |
| 4 # Licensed under the Apache License, Version 2.0 (the "License"); | |
| 5 # you may not use this file except in compliance with the License. | |
| 6 # You may obtain a copy of the License at | |
| 7 # | |
| 8 # http://www.apache.org/licenses/LICENSE-2.0 | |
| 9 # | |
| 10 # Unless required by applicable law or agreed to in writing, software | |
| 11 # distributed under the License is distributed on an "AS IS" BASIS, | |
| 12 # WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. | |
| 13 # See the License for the specific language governing permissions and | |
| 14 # limitations under the License. | |
| 15 | |
| 16 """Helper methods for creating & verifying XSRF tokens.""" | |
| 17 | |
| 18 import base64 | |
| 19 import binascii | |
| 20 import hmac | |
| 21 import time | |
| 22 | |
| 23 from oauth2client._helpers import _to_bytes | |
| 24 from oauth2client import util | |
| 25 | |
| 26 __authors__ = [ | |
| 27 '"Doug Coker" <dcoker@google.com>', | |
| 28 '"Joe Gregorio" <jcgregorio@google.com>', | |
| 29 ] | |
| 30 | |
| 31 # Delimiter character | |
| 32 DELIMITER = b':' | |
| 33 | |
| 34 # 1 hour in seconds | |
| 35 DEFAULT_TIMEOUT_SECS = 60 * 60 | |
| 36 | |
| 37 | |
| 38 @util.positional(2) | |
| 39 def generate_token(key, user_id, action_id='', when=None): | |
| 40 """Generates a URL-safe token for the given user, action, time tuple. | |
| 41 | |
| 42 Args: | |
| 43 key: secret key to use. | |
| 44 user_id: the user ID of the authenticated user. | |
| 45 action_id: a string identifier of the action they requested | |
| 46 authorization for. | |
| 47 when: the time in seconds since the epoch at which the user was | |
| 48 authorized for this action. If not set the current time is used. | |
| 49 | |
| 50 Returns: | |
| 51 A string XSRF protection token. | |
| 52 """ | |
| 53 digester = hmac.new(_to_bytes(key, encoding='utf-8')) | |
| 54 digester.update(_to_bytes(str(user_id), encoding='utf-8')) | |
| 55 digester.update(DELIMITER) | |
| 56 digester.update(_to_bytes(action_id, encoding='utf-8')) | |
| 57 digester.update(DELIMITER) | |
| 58 when = _to_bytes(str(when or int(time.time())), encoding='utf-8') | |
| 59 digester.update(when) | |
| 60 digest = digester.digest() | |
| 61 | |
| 62 token = base64.urlsafe_b64encode(digest + DELIMITER + when) | |
| 63 return token | |
| 64 | |
| 65 | |
| 66 @util.positional(3) | |
| 67 def validate_token(key, token, user_id, action_id="", current_time=None): | |
| 68 """Validates that the given token authorizes the user for the action. | |
| 69 | |
| 70 Tokens are invalid if the time of issue is too old or if the token | |
| 71 does not match what generateToken outputs (i.e. the token was forged). | |
| 72 | |
| 73 Args: | |
| 74 key: secret key to use. | |
| 75 token: a string of the token generated by generateToken. | |
| 76 user_id: the user ID of the authenticated user. | |
| 77 action_id: a string identifier of the action they requested | |
| 78 authorization for. | |
| 79 | |
| 80 Returns: | |
| 81 A boolean - True if the user is authorized for the action, False | |
| 82 otherwise. | |
| 83 """ | |
| 84 if not token: | |
| 85 return False | |
| 86 try: | |
| 87 decoded = base64.urlsafe_b64decode(token) | |
| 88 token_time = int(decoded.split(DELIMITER)[-1]) | |
| 89 except (TypeError, ValueError, binascii.Error): | |
| 90 return False | |
| 91 if current_time is None: | |
| 92 current_time = time.time() | |
| 93 # If the token is too old it's not valid. | |
| 94 if current_time - token_time > DEFAULT_TIMEOUT_SECS: | |
| 95 return False | |
| 96 | |
| 97 # The given token should match the generated one with the same time. | |
| 98 expected_token = generate_token(key, user_id, action_id=action_id, | |
| 99 when=token_time) | |
| 100 if len(token) != len(expected_token): | |
| 101 return False | |
| 102 | |
| 103 # Perform constant time comparison to avoid timing attacks | |
| 104 different = 0 | |
| 105 for x, y in zip(bytearray(token), bytearray(expected_token)): | |
| 106 different |= x ^ y | |
| 107 return not different | |
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