Preview package, officially released here
Package contains Anjay LwM2M client library along with necessary components: X-CUBE-CELLULAR, mbedTLS, LwIP for developement under STM32CubeMX environment.
For instructions regarding importing the package, projects configuration and creation please visit AVSystem Developer Zone.
Once the package is imported in STM32CubeMX (according to the guide in the link above), you can find documentation inside it as well.