started off just on sharing credentials across S3A and S3Guard, but in the process it has grown to becoming one of stabilising the assumed role support so it can be used for more than just testing.
Was: "S3Guard to get AWS Credential chain from S3AFS; credentials closed() on shutdown"
S3Guard builds its DDB auth chain itself, which stops it having to worry about being created standalone vs part of an S3AFS, but it means its authenticators are in a separate chain.
When you are using short-lived assumed roles or other session credentials updated in the S3A FS authentication chain, you need that same set of credentials picked up by DDB. Otherwise, at best you are doubling load, at worse: the DDB connector may not get refreshed credentials.
Proposed: DynamoDBClientFactory.createDynamoDBClient() to take an optional ref to aws credentials. If set: don't create a new set.
There's one little complication here: our AWSCredentialProviderList list is autocloseable; it's close() will go through all children and close them. Apparently the AWS S3 client (And hopefully the DDB client) will close this when they are closed themselves. If DDB has the same set of credentials as the FS, then there could be trouble if they are closed in one place when the other still wants to use them.
Solution; have a use count the uses of the credentials list, starting at one: every close() call decrements, and when this hits zero the cleanup is kicked off