nova/doc/api_samples/os-security-groups/security-group-rules-post-req.json

{
    "security_group_rule": {
        "parent_group_id": "21111111-1111-1111-1111-111111111112",
        "ip_protocol": "tcp",
        "from_port": 22,
        "to_port": 22,
        "cidr": "10.0.0.0/24"
    }
}