fix: Fix encryption key in OAuth2 class

src/nbiatoolkit/auth.py

@@ -111,7 +111,7 @@ def __init__(
         self._fernet_key: bytes = Fernet.generate_key()
         self.username: str
         self.password: str
-        self.username, self.password = encrypt_credentials(key=self.fernet_key, username=username, password=password)
+        self.username, self.password = encrypt_credentials(key=self._fernet_key, username=username, password=password)
 
         if isinstance(base_url, NBIA_ENDPOINTS):
             self.base_url = base_url.value
@@ -125,10 +125,6 @@ def __init__(
         self.scope = None
 
 
-    @property
-    def fernet_key(self) -> bytes:
-        return self._fernet_key
-
     def is_logged_out(self) -> bool:
         return (self._access_token is "" and self.username == "" and self.password == "" and self.client_id == "" and self.base_url == "")