Cloud Computing is a new computing paradigm. Among the incredible number of challenges in this field two of them are considered of great relevance: SLA management and Security management. The level of trust in such context is very hard to define and is strictly related to the problem of management of SLA in cloud applications and providers. In this paper we will try to show how it is possible, using a cloud-oriented API derived from the mOSAIC project, to build up an SLA-oriented cloud application which enables the management of security features related to user authentication and authorization to an Infrastructure as a Service (IaaS) Cloud Provider. As Cloud Provider we will adopt the perf-Cloud solution, which uses GRID-based solutions for security management and service delivery. So the proposed solution can be used in order to build up easily a SLA-based interface for any GRID system.