aws role based policy understanding

In this setup, you create a role and then give it some permission. Then whenever a user would like to use it, they assume this role. Typically this can be done simply 

aws sts assume-role --role-arn arn:aws:iam::my-aws-id:role/s3-power-user --role-session-name jeremy-session

And you can test it out simply by running the following commands:-

aws s3 ls s3://appjerwo-demo-test

aws s3 cp test.txt s3://appjerwo-demo-test/ 

aws s3 cp s3://appjerwo-demo-test/test.txt . 

A typical policy would look like this. The key here is Action: "sts:AssumeRole".

{

    "Version": "2012-10-17",

    "Statement": [

        {

            "Effect": "Allow",

            "Principal": {

                "AWS": "arn:aws:iam::(my-aws-id):root"

            },

            "Action": "sts:AssumeRole",

            "Condition": {}

        }

    ]

}