Abstract: Systems and methods are described for authenticating parties who communicate via unauthenticated channels. A user authentication verification service receives a request to confirm the identity of a party who communicates via an unauthenticated channel. The user authentication verification service may identify a computing device associated with the claimed user identity, and may determine that the computing device (or an application installed on the computing device) can be used to authenticate the user. The user authentication verification service may thus transmit a push notification or other request to the computing device to request authentication from the user that the party claims to be or represent. The user authentication verification service may then receive information from the computing device, confirm that the information authenticates that the party is the user (or is acting on behalf of the user), and authorize communication via the unauthenticated channel.