S3 Bucket Policy to Allow access to specific users and restrict all

Question

I searched through existing questions and couldnt find an answer. Hence posting here.

I want to restrict access to a S3 bucket to all users except select few users u

Answer 1

To achieve what you want, use an explicit deny with a "NotPrincipal" policy element. The policy below will ensure no other user can access the buckets other than the users listed in the "NotPrincipal" element.

    {
            "Id": "bucketPolicy",
            "Statement": [
                    {
                            "Action": "s3:*",
                            "Effect": "Deny",
                            "NotPrincipal": {
                                    "AWS": [
                                            "arn:aws:iam::1234567890:user/alloweduser"
                                    ]
                            },
                            "Resource": [
                                    "arn:aws:s3:::examplebucket",
                                    "arn:aws:s3:::examplebucket/*"
                            ]
                    }
            ],
            "Version": "2012-10-17"
    }