fix(crypto): correct HKDF key stretching to use HKDF-expand with proper info strings

bitwarden_client.py

@@ -252,10 +252,20 @@ class BitwardenClient:
 
         # Get encrypted user key
         enc_user_key = result.get("Key")
+        _debug(f"[LOGIN] enc_user_key present: {enc_user_key is not None}")
         if enc_user_key:
-            self.enc_key, self.mac_key = self.crypto.decrypt_user_key(
-                enc_user_key, master_key
-            )
+            _debug(f"[LOGIN] enc_user_key (first 40): {enc_user_key[:40]}...")
+            _debug(f"[LOGIN] attempting to decrypt user key with master_key...")
+            try:
+                self.enc_key, self.mac_key = self.crypto.decrypt_user_key(
+                    enc_user_key, master_key
+                )
+                _debug(f"[LOGIN] user key decrypted successfully!")
+                _debug(f"[LOGIN] enc_key (first 8 b64): {b64encode(self.enc_key[:8]).decode()}")
+                _debug(f"[LOGIN] mac_key (first 8 b64): {b64encode(self.mac_key[:8]).decode()}")
+            except Exception as e:
+                _debug(f"[LOGIN] user key decryption FAILED: {e}")
+                raise
             return {
                 "success": True,
                 "master_key": master_key,