Support for authentication without authorisation

A consequence of defining ServerRealm and and xxServiceKey in the (virtual) host configuration is that mod_arpa2_access.so is activated everywhere underneath. This can be a bit much. The setting Require valid-user triggers it and Require all granted does not, but the latter also stops authentication.

We need a solution for places where an identity is required, without Access Control. That might be needed to lookup data for an account, for example, but there need not be constraints on all parts of those accounts.

Suggestion is to change the error No DocumentAccessName or CommunicationAccessName! into a shrugging observation that nothing needs to be done for authorisation.

BTW, it is not handy when both are present. This can result from merging contexts, and easily lead to confusion that take a lot of time to debug. That may be something to report as an error?