def set_iat(self, claim: str = "iat", at_time: Optional[datetime] = None) -> None:
        """
        Updates the time at which the token was issued.

        See here:
        https://tools.ietf.org/html/rfc7519#section-4.1.6
        """
        if at_time is None:
            at_time = self.current_time

        self.payload[claim] = datetime_to_epoch(at_time)

        Updates the time at which the token was issued.

        See here:
        https://tools.ietf.org/html/rfc7519#section-4.1.6
        
rest_framework_simplejwt/tokens.py