implement salt in WAMPCRA authenticate

wampproto/auth/wampcra.py

@@ -18,10 +18,31 @@ def __init__(self, authid: str, secret: str, auth_extra: dict = None):
         self._secret = secret
 
     def authenticate(self, challenge: messages.Challenge) -> messages.Authenticate:
-        signed = sign_wampcra_challenge(challenge.extra["challenge"], self._secret.encode())
+        salt = challenge.extra.get("salt", None)
+        iterations = challenge.extra.get("iterations", 0)
+        key_length = challenge.extra.get("keylen", 32)
+
+        if salt is not None:
+            raw_secret = derive_cra_key(salt, self._secret, iterations, key_length)
+        else:
+            raw_secret = self._secret.encode()
+
+        signed = sign_wampcra_challenge(challenge.extra["challenge"], raw_secret)
         return messages.Authenticate(AuthenticateFields(signed, {}))
 
 
+def derive_cra_key(salt_str: str, secret: str, iterations: int, key_length: int) -> bytes:
+    salt = salt_str.encode("utf-8")
+    secret_bytes = secret.encode("utf-8")
+
+    iterations = iterations if iterations > 0 else 1000
+    key_length = key_length if key_length > 0 else 32
+
+    derived_key = hashlib.pbkdf2_hmac("sha256", secret_bytes, salt, iterations, key_length)
+
+    return base64.b64encode(derived_key)
+
+
 def utcnow() -> str:
     ts = datetime.datetime.utcnow()
     return f"{ts.strftime('%Y-%m-%dT%H:%M:%S.%f')[:-3]}Z"