{
    "Version": "2012-10-17",
    "Statement": [
        {
            "Effect": "Allow",
            "Action": "s3:*",
            "Resource": [
                "arn:aws:s3:::mybucket/toto3/*"
            ]
        },
        {
            "Effect": "Allow",
            "Action": [
                "s3:ListAllMyBuckets",
                "s3:GetBucketLocation"
            ],
            "Resource": "arn:aws:s3:::*"
        },
        {
            "Effect": "Allow",
            "Action": "s3:ListBucket",
            "Resource": "arn:aws:s3:::mybucket",
            "Condition": {
                "StringLike": {
                    "s3:prefix": [
                        "",
                        "toto3/",
                        "toto3*"
                    ]
                }
            }
        }
    ]
}
https://stackoverflow.com/questions/35944349/iam-aws-s3-to-restrict-to-a-specific-sub-folder