This document proposes a novel authentication solution for MapReduce (MR) models deployed in public clouds. It begins by describing the MR model and job execution workflow. It then discusses security issues with deploying MR in open environments like clouds. Next, it specifies requirements for an MR authentication service, including entity identification, credential revocation, and authentication of clients, MR components, and data. It analyzes existing MR authentication methods and finds they do not fully address the needs of cloud-based MR deployments. The paper then proposes a new "layered authentication solution" with a "virtual domain based authentication framework" to better satisfy the requirements.