Is it permissible to keep illegal aid in a secular country under the pretext of taxes being taken from one's salary without consent, and is the formal consent to tax law considered one of the conditions of fulfillment commanded by the Messenger of Allah (peace and blessings be upon him)?

The questioner's statement: "These people take his money without his consent" is incorrect. By entering their country with an official visa, he has given them a pledge of security, which obliges him to abide by their laws, unless doing so leads to committing what Allah has forbidden. It is an act of betrayal to take what one is not entitled to from aid conditioned on terms one does not adhere to, and this is a contradiction and a double standard in his behavior. He should commit to paying the prescribed taxes and refrain from taking aid and assistance that he is not legally entitled to, due to the generality of the Prophet's (peace be upon him) saying: "Muslims are bound by their conditions."