For using credential-based access control effectively, recent work identified the need to enforce usage constraints also on credentials. The enforcement of such constraints has not yet been investigated for web applications, although it is relevant when credential-based access control is employed in a web application. This article proposes an approach suitable for enforcing usage constraints on credentials in web applications. More concretely, we present a novel algorithm and an implementation of this algorithm that construct constraint-compliant proofs for credential-based access control policies. We proved that our solution is correct and showed that it is also efficient through extensive experiments.