Support caching secrets to disk between invocations

[Riebart]

When running in cron, say once per minute, it may be desirable to be able to cache the secrets (username, password, tokens) to disk in between invocations, and update as necessary. This is also relevant for being able to store these in another location, such as DynamoDB when running it in a Lambda function via CloudWatch Events.

Providing an export/import of credentials from the Session object would be sufficient.

[jgordon165]

another option would be to setup a sqllite.db file. Pretty easy to initialize using some sort of lazy loader and also wouldn't require opening up access to aws