the authority is the church. catechism 2264/65 the first is your right to self defense. the second is for the defense of your family. some want to limit this to just people in authority but ST JPII doesn’t. he states the common good of the family or of the state.
the bold is mine in 2265 giving us the right to use ARMS
2264 Love toward oneself remains a fundamental principle of morality. Therefore it is legitimate to insist on respect for one’s own right to life. Someone who defends his life is not guilty of murder even if he is forced to deal his aggressor a lethal blow:
2265 Legitimate defense can be not only a right but a grave duty for one who is responsible for the lives of others. The defense of the common good requires that an unjust aggressor be rendered unable to cause harm. For this reason, those who legitimately hold authority also have the right to use arms to repel aggressors against the civil community entrusted to their responsibility.
Pope John Paul II’s encyclical letter, Evangelium Vitae summarizes the issue perfectly.
There are in fact situations in which values proposed by God’s Law seem to involve a genuine paradox. This happens for example in the case of legitimate defence, in which the right to protect one’s own life and the duty not to harm someone else’s life are difficult to reconcile in practice. Certainly, the intrinsic value of life and the duty to love oneself no less than others are the basis of a true right to self-defence. The demanding commandment of love of neighbour, set forth in the Old Testament and confirmed by Jesus, itself presupposes love of oneself as the basis of comparison: “You shall love your neighbour as yourself ” (Mk 12:31). Consequently, no one can renounce the right to self-defence out of lack of love for life or for self. This can only be done in virtue of a heroic love which deepens and transfigures the love of self into a radical self-offering, according to the spirit of the Gospel Beatitudes (cf. Mt 5:38-40). The sublime example of this self-offering is the Lord Jesus himself. Moreover, “legitimate defence can be not only a right but a grave duty for someone responsible for another’s life, the common good of the family or of the State”. [The quotation is from # 2265 in the first edition of the Catechism of the Catholic Church.] Unfortunately it happens that the need to render the aggressor incapable of causing harm sometimes involves taking his life. In this case, the fatal outcome is attributable to the aggressor whose action brought it about, even though he may not be morally responsible because of a lack of the use of reason.