Option to use newer Content-Digest field with sha-512

[TurboEncabulator9000]

The changelog for draft-ietf-httpbis-digest-headers states:

Since draft-ietf-httpbis-digest-headers-07

   *  Introduced Repr-Digest and Want-Repr-Digest, and deprecated Digest
      and Want-Digest.  Use of Structured Fields. #1993, #1919

...

Since draft-ietf-httpbis-digest-headers-05

   ...

   *  Add Content-Digest #1542

Libraries for other languages are using the newer Content-Digest header field:

Content-Digest: sha256=:abc:,sha512=:def:

Would be nice if there was a way to do this here as well, and to select sha512 as the algorithm.