To achieve a meaningful business goal,Web services are combined and connected together based on a predefined workflow. In this distributed configuration, tasks are executed by different entities usually managed by different business partners which makes the security monitoring of the whole business process complex. Indeed, the application of classical monitoring methods is not suitable in this kind of service oriented architecture (SOA) where execution traces collection is generally distributed and security requirements implicate several Web services. In this paper we propose a passive testing approach for SOA, encompassing a non-intrusive module that gathers selected traces for web services in both cases of centralized and decentralized workflows, and also a passive tester that analyzes the distributed collected traces and deduces a verdict concerning the respect of the Web services to their security requirements. Finally we apply the proposed methodology to a Loan Origination Process using BPEL workflow