AWS AppSync Auth Link

The `aws-appsync-auth-link` package provides a specialized Apollo Link for integrating AWS AppSync authentication with Apollo Client in JavaScript and TypeScript applications. It is part of the `aws-mobile-appsync-sdk-js` repository and is currently at version 4.0.2. This link allows developers to configure various AWS AppSync authentication modes, including API Key, AWS IAM, Amazon Cognito User Pools, and OpenID Connect, by injecting the necessary authentication headers into GraphQL requests. Its primary differentiator is its seamless integration with the Apollo Client ecosystem, abstracting away the complexities of signing requests for AppSync. The package's release cadence tends to align with major Apollo Client versions, with a significant jump from v1 to v4 to maintain compatibility with `@apollo/client` v3.x and v4.x, implying potentially infrequent but impactful updates.