1. A method comprising: providing, from a client, authentication information of a user for a first domain and a second domain to a server; receiving, by the client, a set of instructions and cryptographic construct data from the server, the set of instructions including information mapping one or more operations to at least one instruction ID; identifying, by the client, a first instruction ID from the set of instructions corresponding to a first set of one or more operations that are permitted to be used in client-side communication between the first domain and the second domain; generating, by the client, using one or more processors in one or more computer systems, a first message using the cryptographic construct data and including the first instruction ID; and sending the first message to a recipient.