Add authentication log information in documentation

doc/configuration.rst

@@ -254,6 +254,25 @@ This parameter is optional but you must ensure it is set to ``False``
 The default configuration file provided by the ``modoboa-admin.py``
 command is properly configured.
 
+**********************
+Logging authentication
+**********************
+
+To trace login attempts to the web interface, Modoboa uses python
+`SysLogHandler <https://docs.python.org/3/library/logging.handlers.html#logging.handlers.SysLogHandler>`_
+and so you can see in you syslog authentication log file
+(`/var/log/auth.log` in most cases).
+
+Depending to your configuration, you may have to edit the :file:`settings.py` file
+and add `'address': '/dev/log'` to the logging section::
+
+    'syslog-auth': {
+        'class': 'logging.handlers.SysLogHandler',
+        'facility': SysLogHandler.LOG_AUTH,
+        'address': '/dev/log',
+        'formatter': 'syslog'
+    },
+
 ***********************
 External authentication
 ***********************