What is the ruling on a husband having anal intercourse with his wife, and the ruling on a wife refusing or agreeing to that, and is a husband entitled to taunt his wife with her past before marriage?

It is not permissible to have intercourse with a woman anally, and it is not permissible for a woman to obey her husband in this, for there is no obedience to a creature in disobedience to the Creator. However, if 'approaching from the back' is meant as engaging in intercourse vaginally but from the rear, then this is permissible. A husband shaming his wife is an abomination and impermissible, whether for something that has passed or something currently happening. His duty is to advise, not to shame. The wife should remind her husband of Allah and of the Prophet's (peace and blessings of Allah be upon him) saying: "The believer is not a slanderer, nor a curser, nor an obscenely foul-mouthed person." She should also be patient with harm, for in it is expiation for sins and elevation of ranks.