Bedrock. Authentication error when using only awsAccessKey & awsSecretKey

[dev-natalya]

Usage

export const client = new AnthropicBedrock({
  awsRegion: "us-east-1",
  awsAccessKey: "MY_ADMIN_ACCESS_KEY",
  awsSecretKey: "MY_ADMIN_SECRET_ACCESS_KEY",
})

// using SDK, message.create() request using the client above

Problem

Runtime error happens only in a Lambda function, not locally.

PermissionDeniedError: 403 The security token included in the request is invalid

Expected behavior

The error shouldn't happen in the case above.
The SDK does not need awsSessionToken to be provided.
Only the awsAccessKey & awsSecretKey should be required to match aws-sdk (v2/v3) behavior.