The Nordic nRF91 modems include secure storage for TLS credentials. This may be used to authenticate with Golioth. The assets are stored separately from the firmware, and once written, they cannot be read back from the device. This guide shows the process of storing and using credentials.
Vit Prajzler, CTO of Golioth, explains the concept of a Pre-Shared Key (PSK) and how it lends a simple but flexible amount of security for prototypes on the Golioth network. IoT prototypes on the Golioth platform are "Secure by default".