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 python3.5

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utils.py

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import base64

import hmac

def calculate_at_hash(access_token, hash_alg):

"""Helper method for calculating an access token

hash, as described in http://openid.net/specs/openid-connect-core-1_0.html#CodeIDToken

Its value is the base64url encoding of the left-most half of the hash of the octets

of the ASCII representation of the access_token value, where the hash algorithm

used is the hash algorithm used in the alg Header Parameter of the ID Token's JOSE

Header. For instance, if the alg is RS256, hash the access_token value with SHA-256,

then take the left-most 128 bits and base64url encode them. The at_hash value is a

case sensitive string.

Args:

access_token (str): An access token string.

hash_alg (callable): A callable returning a hash object, e.g. hashlib.sha256

"""

hash_digest = hash_alg(access_token.encode('utf-8')).digest()

cut_at = int(len(hash_digest) / 2)

truncated = hash_digest[:cut_at]

at_hash = base64url_encode(truncated)

return at_hash.decode('utf-8')

def base64url_decode(input):

"""Helper method to base64url_decode a string.

Args:

input (str): A base64url_encoded string to decode.

"""

rem = len(input) % 4

if rem > 0:

input += b'=' * (4 - rem)

return base64.urlsafe_b64decode(input)

def base64url_encode(input):

"""Helper method to base64url_encode a string.

Args:

input (str): A base64url_encoded string to encode.

"""

return base64.urlsafe_b64encode(input).replace(b'=', b'')

def timedelta_total_seconds(delta):

"""Helper method to determine the total number of seconds

from a timedelta.

Args:

delta (timedelta): A timedelta to convert to seconds.

"""

return delta.days * 24 * 60 * 60 + delta.seconds

def constant_time_string_compare(a, b):

"""Helper for comparing string in constant time, independent

of the python version being used.

Args:

a (str): A string to compare

b (str): A string to compare

"""

try:

return hmac.compare_digest(a, b)

except AttributeError:

if len(a) != len(b):

return False

result = 0

for x, y in zip(a, b):

result |= ord(x) ^ ord(y)

return result == 0