Article by Nick Frichette.
Whoami - Get Principal Name From Keys
Original Research: Spencer Gietzen
As of August 15, 2020 these calls are now tracked in CloudTrail (tweet). This page is maintained for historical and inspiration purposes.
As found by Spencer Gietzen, the API call for sdb list-domains will return very similar information to get-caller-identity.
user@host:$ aws sdb list-domains --region us-east-1 An error occurred (AuthorizationFailure) when calling the ListDomains operation: User (arn:aws:sts::123456789012:assumed-role/example_role/i-00000000000000000) does not have permission to perform (sdb:ListDomains) on resource (arn:aws:sdb:us-east-1:123456789012:domain/). Contact account owner.