[core] Adjust cw<3.21 compatibility
Most of cubibweb < 3.21 expects a ClientConnection as the main connection.
Related to #5731814
Closes #5878592
.. _authplugin_module:
:mod:`pyramid_cubicweb.authplugin`
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.. automodule:: pyramid_cubicweb.authplugin
.. autoclass:: DirectAuthentifier
:show-inheritance:
:members: