Pluggable Remote User

Select the code to handle REMOTE_USER based on a config file option

Fixes the REMOTE_USER logic to get the domain name from
REALM, which is the least surprise option.

Disregards the auth_data passed in, as we should be using REMOTE_USER
to get the user name.

External Plugin is now executed in conjunction with the auth methods,
as opposed to in place of them.

DocImpact

blueprint pluggable-remote-user

Change-Id: I9dda6dbe073f03806bdf539db6faa01644109f1c
Fix XML rendering with empty auth payload.

Just add some sensible defaults to places where XML parses for example
an empty dictionary as an empty string. Also 'access' shouldn't be
considered a plural.

Change-Id: I9fb2c4f5c32ed8c2ce8ba4038caaae39590f8c1a
Merge "Pluggable Remote User"
Merge "Fix XML rendering with empty auth payload."