Since the beginning of 2019 https://www.arcgis.com rejects connections using TLS 1.0 for security reasons.
CityEngine 2017.1 and earlier are unable to support the now required TLS 1.2 protocol.
What is TLS?
TLS stands for “Transport Layer Security.” It is a protocol that provides privacy and data integrity between two communicating applications. It’s the most widely deployed security protocol used today, and is used for web browsers (i.e. HTTPS) and other applications that require data to be securely exchanged over a network. TLS ensures that a connection to a remote endpoint is the intended endpoint through encryption and endpoint identity verification. The versions of TLS, to date, are TLS 1.0, 1.1 and 1.2.