Amazon S3 Access Grants map identities in directories such as Active Directory, or AWS Identity and Access Management (IAM) Principals, to datasets in S3. This helps you manage data permissions at scale by automatically granting S3 access to end-users based on their corporate identity. Additionally, S3 Access Grants log end-user identity and the application used to access S3 data in AWS CloudTrail. This helps to provide a detailed audit history down to the end-user identity for all access to the data in your S3 buckets.
Source:: Amazon AWS