Final answer:
The question is related to invalid authentication methods for a Principal in OCI IAM service, with examples such as using a simple PIN or social media credentials without additional factors being non-valid in the enterprise context of OCI.
Step-by-step explanation:
The question is asking about methods that are not valid for authenticating a Principal in the Oracle Cloud Infrastructure (OCI) Identity and Access Management (IAM) service. Authentication methods in OCI typically involve confirming the identity of the person or system (Principal) trying to access resources within OCI.
Valid methods of authentication could include using a username and password, API signing keys, OAuth tokens, or federated identities through SAML. However, methods such as using a simple personal identification number (PIN) without any additional factors, or utilizing challenge questions that are not part of a multi-factor authentication, would not typically be considered secure in enterprise environments like OCI.