Political authority is ability of an agent (or agents) to morally compel another to action in a way that is content independent and preemptive. By content independent, it means that you should act just because you were ordered and irrespective of the content (provided of course, that the content was within the scope of the authority); and by preemptive it means that it overrides other reasons for not acting - it’s not just added to a balance of reasons for or against action 1.
Authority differs from power in that it contains a normative claim - that you ought comply with an authoritative directive - and the normative claim is made by the authority them self as opposed to some third party. So a criminal gang may have power - they may order you to hand over your money and threaten you with harm if you fail to comply. Likewise, the state may order you to pay taxes, and threaten you with jail if you refuse. You may have good reasons for complying with both orders - self preservation being a rather compelling one - but only the state is claiming that you have a moral duty to comply.
The reasons the gang give are sufficient for their ends but they appeal purely to your own interests. The state on the other hand, either truly believing that it is, or simply realising that wide spread willing compliance is a necessary condition for its rule, claims that you have an obligation to obey because of consent, fair play, divine right, or some other reason.
It’s useful here to distinguish between authority as a designator, and authority as a noun. We might use authority here to indicate the individual or group claiming a right to rule or an obligation to be obeyed. If their orders are obeyed, they have power, and if they are obeyed simply because they were ordered, we can say that they have authority. This can lead to apparent contradiction however - if an authority lacks the power to ensure compliance with their demands, or its subjects reject the normative claim, then it would seem that the authority has no authority. In cases like these, I’ll use the term claimants as the designator to avoid confusion.
Now whether or not you do in fact have an obligation to obey a political authority - whether or not its directives are actually morally binding - depends on the legitimacy of the authority. That an authority claims its orders are morally binding, and that these ordered are generally obeyed, is sufficient for the claimant to have de facto authority. If however, its orders are in fact morally binding rather than simply claimed to be, then we say that it has de jure authority. Its authority is legitimate, and the coercive threats for non-compliance that accompany its orders are justified.
Leslie Green - The Authority of the State (Clarendon Press 1990) - for example provides a good account political obligation noting that they must be normative, content independent, binding, particular this authority, and universal to its subjects. ↩