erp5_oauth2_authorisation: Drop login retry URL double base64-encoding

Fernet tokens are urlsafe-base64-encoded, so re-encoding them is
useless.

This change breaks compabitility with what should be a transient login state
(lasting as long as the login form is opened in any browser). So the
consequence is that a user failing to authenticate will be redirected to a
safe location (ex: the website's home page) instead of getting to the login
form again.
This should not be worth either a systematic double-decrypting (which could
lead to harder to debug decryption errors) or some heuristic trying to
guess if the value is in fact double-encoded.

bt5/erp5_oauth2_authorisation/DocumentTemplateItem/portal_components/document.erp5.OAuth2AuthorisationServerConnector.py

@@ -25,7 +25,6 @@
 #
 ##############################################################################
 
-import base64
 import contextlib
 from functools import wraps
 from io import BytesIO
@@ -1025,7 +1024,7 @@ class OAuth2AuthorisationServerConnector(XMLObject):
     """
     try:
       login_retry_url = self.__getLoginRetryURLMultiFernet().decrypt(
-        base64.urlsafe_b64decode(REQUEST.form['login_retry_url']),
+        REQUEST.form['login_retry_url'],
       )
     except (fernet.InvalidToken, TypeError, KeyError):
       # No login_retry_url provided or its value is unusable: if this is a GET
@@ -1040,9 +1039,7 @@ class OAuth2AuthorisationServerConnector(XMLObject):
     def getSignedLoginRetryUrl():
       if login_retry_url is None:
         return None
-      return base64.urlsafe_b64encode(
-        self.__getLoginRetryURLMultiFernet().encrypt(login_retry_url),
-      )
+      return self.__getLoginRetryURLMultiFernet().encrypt(login_retry_url)
     return _ERP5AuthorisationEndpoint(
       server_connector_path=self.getPath(),
       zope_request=REQUEST,
@@ -1075,9 +1072,7 @@ class OAuth2AuthorisationServerConnector(XMLObject):
       method=method,
       query_list=query_list + [(
         'login_retry_url',
-        base64.urlsafe_b64encode(
         self.__getLoginRetryURLMultiFernet().encrypt(login_retry_url),
-        ),
       )],
     ) as inner_request:
       # pylint: disable=unexpected-keyword-arg, no-value-for-parameter