Add Fintech SDK Use Case to Privacy Sandbox Sample (e.g., Tap-to-Pay, Authentication, Transaction Flow)

[mat-in]

The existing Privacy Sandbox SDK Runtime samples primarily focus on advertising and general-purpose use cases. However, there is a growing need for guidance tailored to fintech SDKs, which often require high levels of security and privacy. Examples include SDKs for tap-to-pay payments, user authentication, and secure transaction flows.

These SDKs commonly use components such as intents, bound services, and broadcast receivers—features that are restricted within the Privacy Sandbox SDK Runtime. To support the migration of such SDKs, a dedicated sample demonstrating fintech-specific functionality within the constraints of the Privacy Sandbox would be highly beneficial.

I propose adding a sample that includes:

• A secure transaction or payment authorization flow
• Interface definitions using @PrivacySandboxInterface and @PrivacySandboxCallback
• Handling of success, failure, and error callbacks
• UI integration using SandboxedUiAdapter

This would serve as a practical reference for SDK developers working on secure financial applications and help accelerate adoption of the SDK Runtime in regulated domains.