Due, rightful, condign are comparable when they mean being in accordance with what is just and appropriate.
Due, which basically means owed or owing as a debt, carries over in the sense here considered a strong implication that the thing so described is grounded upon an obligation, duty, or debt which should not or cannot be ignored; thus, one who takes due precautions uses the care that is required by his obligation to look out for his own or for others’ safety or well-being; one who has a due sense of another person’s rights accords to that person all that belongs to him by natural or moral right; one who has due respect for the law observes the individual laws as the duty of a responsible citizen.
Often the term implies little more than an accordance with what is right, reasonable, or necessary.
Rightful carries a much stronger and more consistent implication than due of a ground in right and justice, and usually suggests a moral or legal claim.
Condign applies to something that is distinctly deserved or merited and usually something that neither exceeds nor falls below one’s deserts or merits; the term is used chiefly of punishment, often with the implication of severity.