[SPA++] Capability to configure a mount in _cmsinternal to leverage CMS authenticated session

According to rkauffman, the preview resourceapi must be able to share the JCR Session with what CMS uses, instead of a separate preview api mount (e.g, /preview/resourceapi).
See HSTTWO-4240 for detail and please discuss with rkauffman if needed.

So, I guess it should be somehow possible to configure an additional resourceapi mount under /_cmsinternal to be able to share the cms jcr session like channel manager does.

Perhaps it is already possible. In that case, please describe or refer to the instruction.
If something should be improved in HSTTWO level, please proceed.

Thanks.