karabiner.json

{
    "description": "Remap mouse keys",
    "manipulators": [
        {
            "from": {
                "key_code": "spacebar",
                "modifiers": { "mandatory": ["right_control"] }
            },
            "to": [
                {
                    "modifiers": [],
                    "pointing_button": "button1"
                }
            ],
            "type": "basic"
        },
        {
            "from": {
                "key_code": "right_command",
                "modifiers": { "mandatory": ["right_control"] }
            },
            "to": [
                {
                    "modifiers": [],
                    "pointing_button": "button2"
                }
            ],
            "type": "basic"
        }
    ]
}