Which two mechanisms augment OAuth 2.0 for enhanced validation?

OAuth 2.0 is an authorization framework, not an authentication protocol. It allows a user to grant a third-party application limited access to their resources without sharing their credentials. To enhance validation, OAuth 2.0 is often augmented with authentication mechanisms (like OpenID Connect) to verify the user's identity, and authorization mechanisms (like scopes or policies) to define the specific permissions granted. Custom headers and request management are general web development concepts, not specific augmentation mechanisms for OAuth 2.0 validation. Accounting is related to tracking resource usage, not enhancing validation.