Now easily identify the identity responsible for the actions performed using IAM roles
AWS Identity and Access Management (IAM) now makes it easier to identify who is responsible for an AWS action performed by an IAM role when viewing AWS CloudTrail logs. Adding the new service-specific condition, sts:RoleSessionName, in an IAM policy, enables you to define the role session name that must be set when an IAM principal (user or role) or application assumes the IAM role. AWS adds the role session name to the AWS CloudTrail log when the IAM role performs an action, making it easy to determine who performed the action.
Source:: Amazon AWS