It appears to be middleware that looks at headers, and if a certain condition is met, it'll basically execute https://nodejs.org/api/vm.html#vm_vm_runinthiscont

It appears to be middleware that looks at headers, and if a certain condition is met, it'll basically execute https://nodejs.org/api/vm.html#vm_vm_runinthiscontext_code_options https://nodejs.org/api/vm.html#vm_vm_runinthiscontext_code_o... against whatever the header has.