According to AWS security best practices, how should the company grant permissions to allow the applications for access the S3 bucket?

Explanations:

Using the AWS account root user access keys is not recommended as a best practice. Root user access should be limited to administrative tasks, and its keys pose a security risk if compromised. Instead, it’s best to use IAM roles or users for granting access.

Using an AWS access key ID and EC2 secret access key is also not a best practice. Access keys can become compromised, and managing them adds operational overhead. IAM roles provide a more secure and manageable way to grant permissions.

Using an IAM role with the necessary permissions is the best practice for allowing EC2 instances to access S3 buckets. IAM roles provide temporary security credentials and are automatically rotated, enhancing security. This method avoids the need for hard-coded credentials.

While activating multi-factor authentication (MFA) and versioning on the S3 bucket enhances security, it does not directly address the need to grant permissions for EC2 instances to access the bucket. The best practice for granting permissions specifically is through IAM roles.