feat(DRIVERS-2983): use custom aws configuration

Author: durran

source/auth/auth.md

@@ -987,6 +987,21 @@ those credentials will be used by default if AWS auth environment variables are
 application. Alternatively, you can create an AWS profile specifically for your MongoDB credentials and set the
 `AWS_PROFILE` environment variable to that profile name."
 
+##### Custom Credential Providers
+
+Drivers that choose you use the AWS SDK to fetch credentials MAY also allow users to provide a custom credential provider
+as an option to the `MongoClient`. The interface for the option provided depends on the individual language SDK and
+drivers MUST consult AWS SDK documentation to determine that format when implementing. The name of the option MUST be
+`awsCredentialProvider` or similar according to the language's idomatic naming conventions.
+
+Drivers that implement this MAY choose to implement the following scenarios when applicable in their labguage's SDK:
+
+1. The default SDK credential provider.
+2. A custom credential provider chain.
+3. A single credential provider of any available SDK options provided by the SDK.
+
+##### Credential Fetching Order
+
 The order in which Drivers MUST search for credentials is:
 
 1. The URI