Final answer:
The CLI command to create a custom RBAC role from a JSON file is 'az role definition create'.
Step-by-step explanation:
To create a custom RBAC role from a JSON file using the CLI, you can use the az role definition create command. Here is an example of the command:
az role definition create --role-definition "/path/to/custom-role.json"
Make sure you replace "/path/to/custom-role.json" with the actual file path of your JSON file. This command will create a custom role in Azure Active Directory based on the contents of the JSON file.