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awsidp.py
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import base64
import hashlib
import hmac
import os
import binascii
import sys
import json
import datetime
import requests
PY2 = sys.version_info[0] == 2
PY3 = sys.version_info[0] == 3
if PY3:
basestring = str
class AwsIdp:
def __init__(self, pool_id, client_id):
""" Simple AWS Identity Provider client.
:param str pool_id: The AWS user pool to connect to (format: <region>_<poolid>).
E.g.: eu-west-1_aLkOfYN3T
:param str client_id: The client application ID (the ID of the application connecting)
:param ProxyInfo proxy: A proxy info object if needed
The content of this file is a simplification of the Warrent aws_srp.py file.
"""
self.pool_id = pool_id
if "_" not in self.pool_id:
raise ValueError("Invalid pool_id format. Shoud be <region>_<poolid>.")
self.client_id = client_id
self.region = self.pool_id.split("_")[0]
self.url = "https://cognito-idp.%s.amazonaws.com/" % (self.region, )
# Initialize the values
# https://github.com/aws/amazon-cognito-identity-js/blob/master/src/AuthenticationHelper.js#L22
self.n_hex = 'FFFFFFFFFFFFFFFFC90FDAA22168C234C4C6628B80DC1CD1' + \
'29024E088A67CC74020BBEA63B139B22514A08798E3404DD' + \
'EF9519B3CD3A431B302B0A6DF25F14374FE1356D6D51C245' + \
'E485B576625E7EC6F44C42E9A637ED6B0BFF5CB6F406B7ED' + \
'EE386BFB5A899FA5AE9F24117C4B1FE649286651ECE45B3D' + \
'C2007CB8A163BF0598DA48361C55D39A69163FA8FD24CF5F' + \
'83655D23DCA3AD961C62F356208552BB9ED529077096966D' + \
'670C354E4ABC9804F1746C08CA18217C32905E462E36CE3B' + \
'E39E772C180E86039B2783A2EC07A28FB5C55DF06F4C52C9' + \
'DE2BCBF6955817183995497CEA956AE515D2261898FA0510' + \
'15728E5A8AAAC42DAD33170D04507A33A85521ABDF1CBA64' + \
'ECFB850458DBEF0A8AEA71575D060C7DB3970F85A6E1E4C7' + \
'ABF5AE8CDB0933D71E8C94E04A25619DCEE3D2261AD2EE6B' + \
'F12FFA06D98A0864D87602733EC86A64521F2B18177B200C' + \
'BBE117577A615D6C770988C0BAD946E208E24FA074E5AB31' + \
'43DB5BFCE0FD108E4B82D120A93AD2CAFFFFFFFFFFFFFFFF'
# https://github.com/aws/amazon-cognito-identity-js/blob/master/src/AuthenticationHelper.js#L49
self.g_hex = '2'
self.info_bits = bytearray('Caldera Derived Key', 'utf-8')
self.big_n = self.__hex_to_long(self.n_hex)
self.g = self.__hex_to_long(self.g_hex)
self.k = self.__hex_to_long(self.__hex_hash('00' + self.n_hex + '0' + self.g_hex))
self.small_a_value = self.__generate_random_small_a()
self.large_a_value = self.__calculate_a()
self.session = requests.session()
def authenticate(self, username, password):
# Step 1: First initiate an authentication request
auth_request = self.__get_authentication_request(username)
auth_data = json.dumps(auth_request, sort_keys=False, ensure_ascii=False)
auth_headers = {
"X-Amz-Target": "AWSCognitoIdentityProviderService.InitiateAuth",
"Accept-Encoding": "identity",
"Content-Type": "application/x-amz-json-1.1",
"user-agent": "Mozilla/5.0 (Windows; U; Windows NT 6.1; en-GB; rv:1.9.2.13) Gecko/20101203 Firefox/3.6.13 (.NET CLR 3.5.30729)"
}
auth_response = self.session.post(self.url, data=auth_data, headers=auth_headers)
auth_response_json = json.loads(auth_response.content)
challenge_parameters = auth_response_json.get("ChallengeParameters")
challenge_name = auth_response_json.get("ChallengeName")
if not challenge_name == "PASSWORD_VERIFIER":
return None
# Step 2: Respond to the Challenge with a valid ChallengeResponse
challenge_request = self.__get_challenge_response_request(challenge_parameters, password)
challenge_data = json.dumps(challenge_request, sort_keys=False, ensure_ascii=False)
challenge_headers = {
"X-Amz-Target": "AWSCognitoIdentityProviderService.RespondToAuthChallenge",
"Content-Type": "application/x-amz-json-1.1",
"user-agent": "Mozilla/5.0 (Windows; U; Windows NT 6.1; en-GB; rv:1.9.2.13) Gecko/20101203 Firefox/3.6.13 (.NET CLR 3.5.30729)"
}
auth_response = self.session.post(self.url, data=challenge_data, headers=challenge_headers)
auth_response_json = json.loads(auth_response.content)
if "message" in auth_response_json:
return None, None
id_token = auth_response_json.get("AuthenticationResult").get("IdToken")
refresh_token = auth_response_json.get("AuthenticationResult").get("RefreshToken")
return id_token, refresh_token
def renew_token(self, refresh_token):
"""
Sets a new access token on the User using the refresh token. The basic expire time of the
refresh token is 30 days:
http://docs.aws.amazon.com/cognito/latest/developerguide/amazon-cognito-user-pools-using-tokens-with-identity-providers.html
:param str refresh_token: Token to use for refreshing the authorization token.
"""
refresh_request = {
"AuthParameters": {
"REFRESH_TOKEN": refresh_token
},
"ClientId": self.client_id,
"AuthFlow": "REFRESH_TOKEN"
}
refresh_headers = {
"X-Amz-Target": "AWSCognitoIdentityProviderService.InitiateAuth",
"Content-Type": "application/x-amz-json-1.1"
}
refresh_request_data = json.dumps(refresh_request, sort_keys=False, ensure_ascii=False)
refresh_response = self.session.post(self.url,
data=refresh_request_data,
headers=refresh_headers)
refresh_json = json.loads(refresh_response.content)
id_token = refresh_json.get("AuthenticationResult").get("IdToken")
return id_token
def __get_authentication_request(self, username):
"""
:param str username: The username to use
:return: A full Authorization request.
:rtype: dict
"""
auth_request = {
"AuthParameters": {
"USERNAME": username,
"SRP_A": self.__long_to_hex(self.large_a_value)
},
"AuthFlow": "USER_SRP_AUTH",
"ClientId": self.client_id
}
return auth_request
def __get_challenge_response_request(self, challenge_parameters, password):
""" Create a Challenge Response Request object.
:param dict[str,str|imt] challenge_parameters: The parameters for the challenge.
:param str password: The password.
:return: A valid and full request data object to use as a response for a challenge.
:rtype: dict
"""
user_id = challenge_parameters["USERNAME"]
user_id_for_srp = challenge_parameters["USER_ID_FOR_SRP"]
srp_b = challenge_parameters["SRP_B"]
salt = challenge_parameters["SALT"]
secret_block = challenge_parameters["SECRET_BLOCK"]
timestamp = self.__get_current_timestamp()
# Get a HKDF key for the password, SrpB and the Salt
hkdf = self.__get_hkdf_key_for_password(
user_id_for_srp,
password,
self.__hex_to_long(srp_b),
salt
)
secret_block_bytes = base64.standard_b64decode(secret_block)
# the message is a combo of the pool_id, provided SRP userId, the Secret and Timestamp
msg = bytearray(self.pool_id.split('_')[1], 'utf-8') + \
bytearray(user_id_for_srp, 'utf-8') + \
bytearray(secret_block_bytes) + \
bytearray(timestamp, 'utf-8')
hmac_obj = hmac.new(hkdf, msg, digestmod=hashlib.sha256)
signature_string = base64.standard_b64encode(hmac_obj.digest())
challenge_request = {
"ChallengeResponses": {
"USERNAME": user_id,
"TIMESTAMP": timestamp,
"PASSWORD_CLAIM_SECRET_BLOCK": secret_block,
"PASSWORD_CLAIM_SIGNATURE": signature_string.decode("utf-8")
},
"ChallengeName": "PASSWORD_VERIFIER",
"ClientId": self.client_id
}
return challenge_request
def __get_hkdf_key_for_password(self, username, password, server_b_value, salt):
""" Calculates the final hkdf based on computed S value, and computed U value and the key.
:param str username: Username.
:param str password: Password.
:param int server_b_value: Server B value.
:param int salt: Generated salt.
:return Computed HKDF value.
:rtype: object
"""
u_value = self.__calculate_u(self.large_a_value, server_b_value)
if u_value == 0:
raise ValueError('U cannot be zero.')
username_password = '%s%s:%s' % (self.pool_id.split('_')[1], username, password)
username_password_hash = self.__hash_sha256(username_password.encode('utf-8'))
x_value = self.__hex_to_long(self.__hex_hash(self.__pad_hex(salt) + username_password_hash))
g_mod_pow_xn = pow(self.g, x_value, self.big_n)
int_value2 = server_b_value - self.k * g_mod_pow_xn
s_value = pow(int_value2, self.small_a_value + u_value * x_value, self.big_n)
hkdf = self.__compute_hkdf(
bytearray.fromhex(self.__pad_hex(s_value)),
bytearray.fromhex(self.__pad_hex(self.__long_to_hex(u_value)))
)
return hkdf
def __compute_hkdf(self, ikm, salt):
""" Standard hkdf algorithm
:param {Buffer} ikm Input key material.
:param {Buffer} salt Salt value.
:return {Buffer} Strong key material.
"""
prk = hmac.new(salt, ikm, hashlib.sha256).digest()
info_bits_update = self.info_bits + bytearray(chr(1), 'utf-8')
hmac_hash = hmac.new(prk, info_bits_update, hashlib.sha256).digest()
return hmac_hash[:16]
def __calculate_u(self, big_a, big_b):
""" Calculate the client's value U which is the hash of A and B
:param int big_a: Large A value.
:param int big_b: Server B value.
:return Computed U value.
:rtype: int
"""
u_hex_hash = self.__hex_hash(self.__pad_hex(big_a) + self.__pad_hex(big_b))
return self.__hex_to_long(u_hex_hash)
def __generate_random_small_a(self):
""" Helper function to generate a random big integer
:return a random value.
:rtype: int
"""
random_long_int = self.__get_random(128)
return random_long_int % self.big_n
def __calculate_a(self):
""" Calculate the client's public value A = g^a%N with the generated random number a
:return Computed large A.
:rtype: int
"""
big_a = pow(self.g, self.small_a_value, self.big_n)
# safety check
if (big_a % self.big_n) == 0:
raise ValueError('Safety check for A failed')
return big_a
@staticmethod
def __long_to_hex(long_num):
return '%x' % long_num
@staticmethod
def __hex_to_long(hex_string):
return int(hex_string, 16)
@staticmethod
def __hex_hash(hex_string):
return AwsIdp.__hash_sha256(bytearray.fromhex(hex_string))
@staticmethod
def __hash_sha256(buf):
"""AuthenticationHelper.hash"""
a = hashlib.sha256(buf).hexdigest()
return (64 - len(a)) * '0' + a
@staticmethod
def __pad_hex(long_int):
""" Converts a Long integer (or hex string) to hex format padded with zeroes for hashing
:param int|str long_int: Number or string to pad.
:return Padded hex string.
:rtype: str
"""
# noinspection PyTypeChecker
if not isinstance(long_int, basestring):
hash_str = AwsIdp.__long_to_hex(long_int)
else:
hash_str = long_int
if len(hash_str) % 2 == 1:
hash_str = '0%s' % hash_str
elif hash_str[0] in '89ABCDEFabcdef':
hash_str = '00%s' % hash_str
return hash_str
@staticmethod
def __get_random(nbytes):
random_hex = binascii.hexlify(os.urandom(nbytes))
return AwsIdp.__hex_to_long(random_hex)
@staticmethod
def __get_current_timestamp():
""" Creates a timestamp with the correct English format.
:return: timestamp in format 'Sun Jan 27 19:00:04 UTC 2019'
:rtype: str
"""
# We need US only data, so we cannot just do a strftime:
# Sun Jan 27 19:00:04 UTC 2019
months = [None, 'Jan', 'Feb', 'Mar', 'Apr', 'May', 'Jun', 'Jul', 'Aug', 'Sep', 'Oct', 'Nov', 'Dec']
days = ['Mon', 'Tue', 'Wed', 'Thu', 'Fri', 'Sat', 'Sun']
time_now = datetime.datetime.utcnow()
if sys.platform.startswith('win'):
format_string = "{} {} %#d %H:%M:%S UTC %Y".format(days[time_now.weekday()], months[time_now.month])
else:
format_string = "{} {} %-d %H:%M:%S UTC %Y".format(days[time_now.weekday()], months[time_now.month])
time_string = datetime.datetime.utcnow().strftime(format_string)
return time_string
def __str__(self):
return "AWS IDP Client for:\nRegion: %s\nPoolId: %s\nAppId: %s" % (
self.region, self.pool_id.split("_")[1], self.client_id
)