
Explanation:

Box 1: Service principal
Applications and container orchestrators can perform unattended, or "headless," authentication by using an Azure Active Directory (Azure AD) service principal.
Box 2: AcrPush
AcrPush provides pull/push permissions only and meets the principle of least privilege.
Reference:
https://docs.microsoft.com/en-us/azure/container-registry/container-registry-authentication?tabs=azure-cli
https://docs.microsoft.com/en-us/azure/container-registry/container-registry-roles?tabs=azure-cli