Better Auth Custom Credentials Plugin

This package provides a plugin for the `better-auth` library, enabling highly customizable credentials-based authentication. It allows developers to integrate `better-auth` with virtually any backend authentication system, such as Rails, Django, custom APIs, or LDAP, while leveraging `better-auth`'s existing session management infrastructure. Currently at version 0.1.8, the library is in active development, meaning minor versions may introduce breaking changes to its API. Key differentiators include the ability to define flexible input schemas using Zod for robust validation, store arbitrary custom data (like JWTs or permissions) directly within `better-auth` sessions, configure auto sign-up features, and set custom session expiry per authentication method. It offers a comprehensive solution for adapting diverse authentication logic to the `better-auth` ecosystem.