> Aztec.nr API reference, v6.0.0 (mainnet and testnet). Index: https://docs.aztec.network/aztec-nr-api/v6.0.0/llms.txt

# Function authorize_once

Module: `noir_aztec::macros::functions`

```rust
pub comptime fn authorize_once(
    f: FunctionDefinition,
    from_arg_name: CtString,
    nonce_arg_name: CtString,
)
```

Restricts access to an [`external`](/aztec-nr-api/v6.0.0/noir_aztec/macros/functions/fn.external.md) private or public function so that it can only be called by an authorized account.

Receives the name of a `from` `AztecAddress` variable which will be the default authorized account, and the name of a `nonce` `Field` variable which is used by `from` to grant one-time-only access to other accounts.

## Usage

The `from` account can always call an [`authorize_once`](/aztec-nr-api/v6.0.0/noir_aztec/macros/functions/fn.authorize_once.md) function by passing a value of 0 as the `nonce`. Any other caller requires explicit permission granted by the `from` account, which 1) will be tied to a specific `nonce` value that must be passed by the caller, and which can only be used once, and 2) will restrict all other function params to be exactly the ones that have been authorized by `from`.

## Cost

Private functions perform a private authwit check by calling the standard account contract `verify_private_authwit` function on `from` with the hash resulting of all function params and the nonce. A nullifier is then emitted, preventing the same permission from being used again. Note that this requires that the caller has access to `from`'s contract class ID and salted initialization hash, as it would otherwise not be possible to call the `verify_private_authwit` function.

Public functions call the `consume` function on the `AuthRegistry` contract, which requires that either a) `from` first calls the `set_authorized` public function, or b) that a private authwit check by `from` is passed for the registry's `set_authorized_private` function, allowing in turn the caller to privately call `set_authorized_private` in the same transaction in which the [`authorize_once`](/aztec-nr-api/v6.0.0/noir_aztec/macros/functions/fn.authorize_once.md) function is invoked.