Do you know what exactly constitutes a backdoor and how exactly Australian government "orders" their citizen to add this backdoor ? I less worried about an ind

Do you know what exactly constitutes a backdoor and how exactly Australian government "orders" their citizen to add this backdoor ? I less worried about an individual writing backdoor code and more worried about sabotage by giving private keys to government, leaking sensitive data etc. while these are not strictly backdoors in technical sense I guess government can put such things under that broad category. Another question I have in my mind is whether it would be legal to post "Australian citizens may not apply for this job" under the job posting in USA. Clearly there is a good reason to believe an Australian citizen is not good enough for tech jobs given that he comes with this baggage.