An IAM principal represents an entity that is allowed or denied access to AWS resources. It can be any of the following:

1. IAM User: A human user with AWS credentials.
2. IAM Role: An identity that trusts another authenticated identity to assume its permissions.
3. AWS Service: A service within AWS that interacts with resources.
4. Anonymous User: In specific cases, access can be granted to anonymous users.

How It Works

• Principals are specified in policy statements, granting or denying permissions to specific entities.
• Resource-based policies (e.g., S3 bucket policies) use the Principal element.
• Identity-based policies (attached to IAM users, groups, or roles) implicitly use the identity as the principal.

Benefits:

1. Granular Access Control: Fine-tune permissions for different entities.
2. Cross-Account Access: Enable trusted accounts to assume roles.
3. Temporary Permissions: Roles allow temporary access via session tokens.
4. Least Privilege: Assign only necessary permissions to each principal.

Limitations:

1. No User Groups as Principals: Groups relate to permissions, not authentication.
2. No Wildcards in Principal Names: Cannot match part of a principal name or ARN.

Features:

1. Role Trust Policies: Specify who can assume an IAM role.