The next generation of wireless access systems (5G) aims to improve the Quality of Experience (QoE) for critical services, as well as to provide high availability, low latency, elasticity, and increased security [1]. SDN, NFV and Network Slicing are new concepts and technologies that have emerged as 5G enablers. These technologies can be leveraged to provide Security as a Service (SECaaS) by deploying Security Virtualized Network Functions (VNFs) within different slices and ensuring optimal resource provisioning to reduce Operational Expenditures (OPEX) while ensuring the provisioning of the Service Level Agreement (SLA). Furthermore, proper resource allocation is crucial as a malfunctiong security VNF can compromise the network; therefore, a predictive auto-scaling function, implementing application-specific policies, needs to be deployed along with the monitoring and flow control mechanisms. Recent works have investigated solutions to enable autoscaling mechanisms [2], [3], factors that impact the scaling delay [4]–[۶], and mechanisms relying on SDN to enable security functions [7], [8]. Other solutions have focused on the performance evaluation of security VNFs [9]–[۱۳]. To the best knowledge of the authors, no prior work has been taking into account ways to enforce security within 5G slices. This paper proposes and evaluates an architecture that leverages both SDN/NFV capabilities to enable SECaaS in multi-cloud environments. The rest of this paper is organized as follows. Section II discusses previous works on the subject of this paper. Section III presents an overview of the proposed architecture for enabling SECaaS. Section IV provides the methodology for our experimental evaluation, and discusses the results. Finally, Section V concludes the paper.