keystone/api-ref/source/v3/samples/admin/credential-update-request.json

{
    "credential": {
        "blob": "{\"access\":\"181920\",\"secrete\":\"secretKey\"}",
        "project_id": "731fc6f265cd486d900f16e84c5cb594",
        "type": "ec2",
        "user_id": "bb5476fd12884539b41d5a88f838d773"
    }
}