The GSA publishes their regulations for registering .gov domains: https://www.gsa.gov/policy-regulations/policy/information-in... . In short, an authorized representative of the agency (head or CIO) needs to send a letter: https://home.dotgov.gov/registration/authorization-templates... . It's safe to assume that, since those partitions were created as part of a federal contract, those letters were a normal part of the buildout.