Add support for sending bearer token in the POST body.

Note that reading the request body would be a blocking operation, so this should likely be configured behind a flag of sorts as opposed to being default behavior.

Comment From: jgrandja

@jzheaux Is this still valid or can it be closed?

Comment From: jzheaux

This feature has not yet been implemented, and it is a gap in the spec, so I imagine it should remain open.