We introduce a distributed, fine-granuled, policy-based resource access control protocol leveraging on Attribute-Based Encryption. The protocol secures the whole access control procedure from the authorization issuer to the resource server providing grant confidentiality, proof of possession, antiforgery and may be implemented through a common web token exchange flow plus a HTTP basic authentication. As such, it may easily map to Cloud computing SaaS paradigms, enabling services integration into a single authorization-centric ecosystem even across multiple identity domains. We also present the results of a performance evaluation on a first prototype implementation.