All perfect praise be to Allaah, The Lord of the Worlds. I testify that there is none worthy of worship except Allaah, and that Muhammad, sallallaahu 'alyhi wa sallam, is His slave and Messenger.
Such authorization is allowed in concluding marriage contracts. The Messenger of Allaah, sallallaahu ‘alayhi wa sallam, authorized An-Najaashi (Negus) to conclude the contract of his marriage to Ramlah bint Abu Sufyaan on his behalf. The story of this marriage is famous. Consequently, it is permissible for a man to authorize his father, brother or others to conclude his marriage contract on his behalf.
Allaah Knows best.