anchor.diff:  %% @doc Look for an Authorization header in the request, and validate
   %% it if it exists.  Returns `{ok, User, UserObj}' if validation
   %% succeeds, or `{error, KeyId, Reason}' if any step fails.
  --spec validate_auth_header(#wm_reqdata{}, term(), pid()) ->
  +-spec validate_auth_header(#wm_reqdata{}, term(), pid(), #context{}) ->
                                     {ok, rcs_user(), riakc_obj:riakc_obj()} |
                                     {error, bad_auth | notfound | no_user_key | term()}.
  -validate_auth_header(RD, AuthBypass, RiakPid) ->
  +validate_auth_header(RD, AuthBypass, RiakPid, Ctx) ->
       AuthHeader = wrq:get_req_header("authorization", RD),
       case AuthHeader of
           undefined ->
  
positive.code:          find_and_auth_user/3,
           find_and_auth_user/4,
           find_and_auth_user/5,
           validate_auth_header/3,
           ensure_doc/2,
           deny_access/2,
           deny_invalid_key/2,
  
negative.code:     case riak_cs_get_fsm:get_next_chunk(FsmPid) of
          {done, Chunk} ->
              ok = riak_cs_stats:update_with_start(object_get, StartTime),
              riak_cs_dtrace:dt_object_return(riak_cs_wm_object, <<"object_get">>,
                                                 [], [UserName, BFile_str]),
              {Chunk, done};
          {chunk, Chunk} ->
  