The current scheme of having auth plugins only able to specify the
X-Auth-Token header via the get_token function is too limited for all
plugins. We need to allow both the case where the plugin wants to
control additional headers, or doesn't set the X-Auth-Token header at
all.
This deprecates the get_token interface in favour of the get_headers
interface. Whilst we should promote using get_headers it is likely that
plugins that only require setting the X-Auth-Token header will continue
to only support the get_token interface.
Change-Id: Ibd750d72acc3ba4fd8a880cad69173248ec4092f
blueprint: generic-plugins
cd552374ca