When upgrading from MaxScale 2.4.x or lower to 2.5.x or higher there is a new requirement for server=<server list>
to be added to the binlogrouter . If this is not included Maxscale gives an Access denied error:

ERROR 1045 (28000): Access denied for user...

It would be great to get a more informational error message, maybe something like "no servers defined for binlogrouter"
see: https://mariadb.com/kb/en/mariadb-maxscale-25-binlogrouter/
"The list of servers where the database users for authentication are loaded must be explicitly configured with the servers or targets parameter."