The way that you add the Amazon S3 object storage repository depends on the Amazon Web Service (AWS) authentication method that you use.
IAM role: You have an AWS account that is attached to an Amazon Elastic Compute Cloud (EC2) virtual machine and you need to back up buckets in the same account.
STS assume role with IAM policy: You have Amazon S3 buckets in different AWS accounts, or you need cross AWS accounts.
Access key and secret key: As a best practice, AWS recommends using IAM roles instead of access keys. For more information, see Security best practices in IAM in the AWS documentation.