feat(DRIVERS-2903): use custom aws configuration

[durran]

Adds section to auth spec on allowing user provided custom credential providers for AWS and notes on testing.

Node implementation: mongodb/node-mongodb-native#4373

• Update changelog.
• Test changes in at least one language driver.
• Test these changes against all server versions and topologies (including standalone, replica set, sharded
  clusters, and serverless).

[jyemin]

Just a few quick edits while I perused this.

[jyemin]

Since this needs to be supported in FLE as well, I think we need to update the FLE spec and specify how to configure the "aws" kms provider. Consider adding a similar property with same semantics to AWSKMSOptions in https://github.com/mongodb/specifications/blob/master/source/client-side-encryption/client-side-encryption.md#kmsproviders.

(While in some drivers you might be able to apply an auth mechanism property to FLE, in Java that isn't possible as auth mechanism properties are associated with a credential, not the MongoClient, and the credential of the MongoClient might not even be an AWS credential (or could be a different one).

[durran]

Since this needs to be supported in FLE as well, I think we need to update the FLE spec as well and specify how to configure the "aws" kms provider. Consider adding a similar property with same semantics to AWSKMSOptions in https://github.com/mongodb/specifications/blob/master/source/client-side-encryption/client-side-encryption.md#kmsproviders.

(While in some drivers you might be able to apply an auth mechanism property to FLE, in Java that isn't possible as auth mechanism properties are associated with a credential, not the MongoClient, and the credential of the MongoClient might not even be an AWS credential (or could be a different one).

@kevinAlbs Do you have thoughts on this? Would there be a case where auto-encryption could want a different AWS credential provider than the associated MongoClient. (With ClientEncryption this is already possible since it has its own MongoClient)

[baileympearson]

@durran What about users who aren't using AWS authentication for their clients but want to use AWS automatic KMS credential fetching with a custom provider? I don't think Node would support that without a provider option for KMS specifically.

[baileympearson]

@durran What about users who aren't using AWS authentication for their clients but want to use AWS automatic KMS credential fetching with a custom provider? I don't think Node would support that without a provider option for KMS specifically.

[durran]

@durran What about users who aren't using AWS authentication for their clients but want to use AWS automatic KMS credential fetching with a custom provider? I don't think Node would support that without a provider option for KMS specifically.

That's a good point and I think a valid use case. I'll update everything accordingly.