Disclosed are various approaches for facilitating single sign-on (SSO) for third-party services that are accessible through messages (e.g., email) received by a user. A user can receive a message that includes an embedded URL or link that opens in a third-party service that requires authentication. Instead of requiring the user to enter authentication credentials for accessing the third-party service, a tunnel service can be used to intercept requests for authentication and redirect the requests to an identity manager that can issue a SSO token following an authentication of the user and device. Upon supplying the third-party service with the SSO token, the user can access the content associated with the third-party service without entering authentication credentials.