A regression was introduced during the migration to AWS SDK. One used
to be able to provide credentials in multiple ways with the earlier
Rusoto ChainProvider (config file / environment variables). Now one
has to explicitly set the properties.
Use the DefaultCredentialsChain from AWS SDK to restore the previous
functionality.
See
https://docs.rs/aws-config/0.46.0/aws_config/default_provider/credentials/struct.DefaultCredentialsChain.html.
STS provide temporary credentials to access AWS resource. Temporary
credentials include, AccessKeyId, SecretAccessKey and SessionToken.
With session-token property, element will be able to use temporary
credentials. When session-token is not set, element can use long
term credentials.