Mo. Rev. Stat. § 511.100: Confession by attorney in fact.

A judgment by confession may also be rendered against any person for a debt owing upon a note, bond or bill of exchange, under his power of attorney therefor, acknowledged as required of deeds of land for record and filed in the court rendering the judgment, at the time of its rendition, together with the note, bond or bill of exchange, and the affidavit of the plaintiff that the debt is bona fide, for a fair and valuable consideration, and owing after allowing all just credits and setoffs.