public static Optional<User> getRequestUser() {
    Optional<RpcCall> ctx = getCurrentCall();
    return ctx.isPresent() ? ctx.get().getRequestUser() : Optional.empty();
  }
Returns the user credentials associated with the current RPC request or not present if no
credentials were provided.
@return A User
hbase-server/src/main/java/org/apache/hadoop/hbase/ipc/RpcServer.java