How To Grant Access To Only One S3 Bucket Using AWS IAM Policy

Open the IAM console, select "Policies" under "Access management", and click "Create policy".

In the policy editor, select the "JSON" tab.

Paste the policy below, replacing <your bucket> with your bucket name.

Note: The "s3:ListAllMyBuckets" is used to list all buckets owned by you, so that tools that list buckets will work.
The "s3:GetBucketLocation" is needed so that ObjectiveFS can select the right S3 endpoint to talk with.

Example policy:

{
    "Version": "2012-10-17",
    "Statement": [
        {
            "Effect": "Allow",
            "Action": [
                        "s3:GetBucketLocation",
                        "s3:ListAllMyBuckets"
                      ],
            "Resource": "arn:aws:s3:::*"
        },
        {
            "Effect": "Allow",
            "Action": "s3:*",
            "Resource": [
                "arn:aws:s3:::<your bucket>",
                "arn:aws:s3:::<your bucket>/*"
            ]
        }
    ]
}

Click "Next", enter a policy name, e.g. single-bucket-access, and click "Create policy".

Attach the policy to your IAM user: select "Users", choose your user, and on the "Permissions" tab click "Add permissions". Choose "Attach policies directly", select your new policy, and confirm with "Add permissions".

Note: To grant the same access to several users, attach the policy to a user group instead and add the users to the group.

You can now use your "Access Key ID" and "Secret Access Key" to run ObjectiveFS restricted to a single bucket.