Have to: Modals of Obligation
A modal verb is a type of auxiliary (helping) verb that has no meaning on its own but it modifies the main verb, changes its meaning and gives more details about actions. Have to is a type of auxiliary modal verb used to express certainty, necessity or strong obligation which comes from outside, from external factors. https://open.books4languages.com/english-a2-grammar/chapter/have-to-modals-of-obligation/