feat(NODE-5939): Implement 6.x: cache the AWS credentials provider in the MONGODB-AWS auth logic

[alenakhineika]

Description

Cashing credentials is required by the spec.

The AWS credentials provider instance itself is implemented as a smart credentials cache. It will issue at most one request to IMDS, and will only issue another request when the credentials are about to expire.

Instead of creating a new AWS provider for each authentication, we cache the AWS credentials provider per client.

What is changing?

• Refactor AUTH_PROVIDERS to have factory functions instead of creating providers

• Create instances of auth providers in MongoClient and cache them when requested per client to ensure that cached credentials are not shared with other clients

  • Expose the getAuthProvider() function per ClientOptions, so it can be requested by connection and monitoring to communicate with auth providers
  • A client can have more than one auth provider because while connecting we can e.g. switch from MONGODB_DEFAULT to MONGODB_SCRAM_SHA256

• Cache AWS provider per MongoDBAWS. AWS SDK will cache the first HTTP request as long as the provider is not reconstructed. We refactor the codebase to ensure that the AWS provider is stored per the MongoDBAWS instance to prevent overwhelming the auth endpoint

Is there new documentation needed for these changes?

None

What is the motivation for this change?

NODE-5616

Release Highlight

Caching AWS credentials provider per client

Instead of creating a new AWS provider for each authentication, we cache the AWS credentials provider per client to prevent overwhelming the auth endpoint and ensure that cached credentials are not shared with other clients.

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