Techniques disclosed herein relate to the authentication of a first user in a communication session between the first user using a user device and a second user using a remote computer system. The computer system sends an authentication request in the session, and the user device receives the authentication request in the session via a messaging program. The user device then causes a different program to access an authentication token received from an authentication computer system. The user device sends an indication of the authentication token to the remote computer system which the remote computer system verifies to authenticate the first user within the session.