Implementing Capability Pattern for Object Authorization

In this tutorial, we will demonstrate how to implement the capability pattern for authorizing actions with an object in the Sui ecosystem. The capability pattern allows you to authorize specific actions using a custom capability type. In our example, we will create a custom NFT-like type Item and an AdminCap capability to control the creation of new Item instances.

Follow these steps to implement the capability pattern:

1. Define the custom type and capability: Create a custom type Item with properties id and name. Define a capability AdminCap with a property id to represent the capability to create new Items.

struct AdminCap has key { id: UID }
 
struct Item has key, store { id: UID, name: String }

2. Initialize the module: Create a module initializer function that is called once on module publish. Inside this function, create an instance of AdminCap and send it to the publisher.

fun init(ctx: &mut TxContext) {
    transfer::transfer(AdminCap {
        id: object::new(ctx)
    }, tx_context::sender(ctx))
}

3. Define the entry function: Create an entry function create_and_send that takes AdminCap, name, and to as arguments. This function cannot be called if AdminCap is not passed as the first argument, ensuring that only the owner of the AdminCap can perform this action.

public entry fun create_and_send(
    _: &AdminCap, name: vector<u8>, to: address, ctx: &mut TxContext
) {
    transfer::transfer(Item {
        id: object::new(ctx),
        name: string::utf8(name)
    }, to)
}

By following these steps, you can implement the capability pattern for authorizing actions with an object in the Sui ecosystem. In this example, we created a custom NFT-like type Item and an AdminCap capability to control the creation of new Item instances, ensuring that only the owner of the AdminCap can create new items.