Method, system, and computer code for implementing security and privacy policy in a web application having an execution environment in which a representation of each object handled by the execution environment accommodates data and an associated tag. An inbound tagging rule is established for tagging inbound objects according to a respective source of each of the inbound objects. A tag is assigned to an object being operated on by the execution environment based on the inbound tagging rule. A security/privacy rule is established for performing security/privacy actions on outbound objects according to a respective tag of each of the outbound objects. A security/privacy action is performed on the object being operated on by the execution environment based on the security/privacy rule.