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Use secrets.choice() instead of random.sample() for PKCE, nonce, and state generation #889

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Use secrets.choice() instead of random.sample() for PKCE, nonce, and state generation #889

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Copilot Mar 19, 2026
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Replace random.sample() with secrets.choice() for PKCE, nonce, and st…
Copilot Mar 19, 2026
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6 changes: 3 additions & 3 deletions msal/oauth2cli/oauth2.py
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Original file line number Diff line number Diff line change
Expand Up @@ -13,7 +13,7 @@
import base64
import sys
import functools
import random
import secrets
import string
import hashlib

Expand Down Expand Up @@ -278,7 +278,7 @@ def _scope_set(scope):
def _generate_pkce_code_verifier(length=43):
assert 43 <= length <= 128
verifier = "".join( # https://tools.ietf.org/html/rfc7636#section-4.1
random.sample(string.ascii_letters + string.digits + "-._~", length))
secrets.choice(string.ascii_letters + string.digits + "-._~") for _ in range(length))
code_challenge = (
# https://tools.ietf.org/html/rfc7636#section-4.2
base64.urlsafe_b64encode(hashlib.sha256(verifier.encode("ascii")).digest())
Expand Down Expand Up @@ -488,7 +488,7 @@ def initiate_auth_code_flow(
raise ValueError('response_type="token ..." is not allowed')
pkce = _generate_pkce_code_verifier()
flow = { # These data are required by obtain_token_by_auth_code_flow()
"state": state or "".join(random.sample(string.ascii_letters, 16)),
"state": state or "".join(secrets.choice(string.ascii_letters) for _ in range(16)),
"redirect_uri": redirect_uri,
"scope": scope,
}
Expand Down
4 changes: 2 additions & 2 deletions msal/oauth2cli/oidc.py
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Original file line number Diff line number Diff line change
@@ -1,7 +1,7 @@
import json
import base64
import time
import random
import secrets
import string
import warnings
import hashlib
Expand Down Expand Up @@ -238,7 +238,7 @@ def initiate_auth_code_flow(
# Here we just automatically add it. If the caller do not want id_token,
# they should simply go with oauth2.Client.
_scope.append("openid")
nonce = "".join(random.sample(string.ascii_letters, 16))
nonce = "".join(secrets.choice(string.ascii_letters) for _ in range(16))
flow = super(Client, self).initiate_auth_code_flow(
scope=_scope, nonce=_nonce_hash(nonce), **kwargs)
flow["nonce"] = nonce
Expand Down
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