rgw: Document fields for access/secret key

The field name mapping for access vs secret key is not clear, this
helped in debugging.

Signed-off-by: Robin H. Johnson <robbat2@gentoo.org>
rgw: Fix signature variable naming/failure print

The signature variables for expected vs got are poorly named, and this
lead them being swapped in the signature validation failure print.
Change them to 'expected' and 'received' and make the related temporary
variables consistent to match.

Signed-off-by: Robin H. Johnson <robbat2@gentoo.org>
rgw: Use correct secret key for POST authn

The POST authentication by signature validation looked up a user based
on the access key, then used the first secret key for the user. If the
access key used was not the first access key, then the expected
signature would be wrong, and the POST would be rejected.

Signed-off-by: Robin H. Johnson <robbat2@gentoo.org>
Merge branch 'bclibcoop/next-cors' of https://github.com/BCLibCoop/ceph into next

Reviewed-by: Yehuda Sadeh <yehuda@inktank.com>