Objection 1. It would seem that one can be dispensed from confessing his sins to a man. For precepts of positive law are subject to dispensation by the prelates of the Church. Now such is confession, as appears from what was said above (Article 3). Therefore one may be dispensed from confession.
Objection 2. Further, a man can grant a dispensation in that which was instituted by a man. But we read of confession being instituted, not by God, but by a man (James 5:16): "Confess your sins, one to another." Now the Pope has the power of dispensation in things instituted by the apostles, as appears in the matter of bigamists. Therefore he can also dispense a man from confessing.
On the contrary, Penance, whereof confession is a part, is a necessary sacrament, even as Baptism is. Since therefore no one can be dispensed from Baptism, neither can one be dispensed from confession.
I answer that, The ministers of the Church are appointed in the Church which is founded by God. Wherefore they need to be appointed by the Church before exercising their ministry, just as the work of creation is presupposed to the work of nature. And since the Church is founded on faith and the sacraments, the ministers of the Church have no power to publish new articles of faith, or to do away with those which are already published, or to institute new sacraments, or to abolish those that are instituted, for this belongs to the power of excellence, which belongs to Christ alone, Who is the foundation of the Church. Consequently, the Pope can neither dispense a man so that he may be saved without Baptism, nor that he be saved without confession, in so far as it is obligatory in virtue of the sacrament. He can, however, dispense from confession, in so far as it is obligatory in virtue of the commandment of the Church; so that a man may delay confession longer than the limit prescribed by the Church.
Reply to Objection 1. The precepts of the Divine law do not bind less than those of the natural law: wherefore, just as no dispensation is possible from the natural law, so neither can there be from positive Divine law.
Reply to Objection 2. The precept about confession was not instituted by a man first of all, though it was promulgated by James: it was instituted by God, and although we do not read it explicitly, yet it was somewhat foreshadowed in the fact that those who were being prepared by John's Baptism for the grace of Christ, confessed their sins to him, and that the Lord sent the lepers to the priests, and though they were not priests of the New Testament, yet the priesthood of the New Testament was foreshadowed in them.
Source: Summa Theologica (New Advent)