Implements `PayinProspect`, a self-contained class that computes suggested donation amounts based on fee tiers (Stripe/PayPal), donor limits, and recipient preferences. It encapsulates fee logic, amount rounding, and minimum/maximum constraints, making it reusable for any payment flow that needs to present donation options to users.

Provides Fernet-based symmetric encryption with automatic key rotation and versioning. The `Cryptograph` class manages multiple encryption keys, supports encrypting/decrypting strings and bytes, and includes a key derivation function. It is isolated from the rest of the codebase and can be extracted for any project requiring secure, rotatable encryption.

Implements a custom CBOR encoder/decoder that handles Python `datetime`, `Decimal`, `Money`, and `MoneyBasket` objects. It extends the standard CBOR library with tag-based encoding for these types, enabling efficient and type-safe serialization for database storage or network transmission. The module is self-contained and demonstrates non-obvious skill in binary serialization.

Defines an abstract base class for OAuth1 and OAuth2 platform integrations, including token management, API request helpers, and user info extraction. It provides a reusable pattern for adding new social login providers with minimal code, as seen in the concrete implementations (GitHub, Twitter, Mastodon, etc.). The module is well-encapsulated and could be extracted as a generic OAuth client library.