EIPs/EIPS/eip-927.md

---
eip: 927
title: Generalised authorisations
author: Nick Johnson <nick@ethereum.org>
type: Standards Track
category: ERC
status: Draft
created: 2018-03-12
requires: 926
---
    
## Abstract
This EIP specifies a generic authorisation mechanism, which can be used to implement a variety of authorisation patterns, replacing approvals in ERC20, operators in ERC777, and bespoke authorisation patterns in a variety of other types of contract.

## Motivation
Smart contracts commonly need to provide an interface that allows a third-party caller to perform actions on behalf of a user. The most common example of this is token authorisations/operators, but other similar situations exist throughout the ecosystem, including for instance authorising operations on ENS domains. Typically each standard reinvents this system for themselves, leading to a large number of incompatible implementations of the same basic pattern. Here, we propose a generic method usable by all such contracts.

The pattern implemented here is inspired by [ds-auth](https://github.com/dapphub/ds-auth) and by OAuth.

## Specification
The generalised authorisation interface is implemented as a metadata provider, as specified in EIP 926. The following mandatory function is implemented:

```
function canCall(address owner, address caller, address callee, bytes4 func) view returns(bool);
```

Where:
 - `owner` is the owner of the resource. If approved the function call is treated as being made by this address.
 - `caller` is the address making the present call.
 - `callee` is the address of the contract being called.
 - `func` is the 4-byte signature of the function being called.

For example, suppose Alice authorises Bob to transfer tokens on her behalf. When Bob does so, Alice is the `owner`, Bob is the `caller`, the token contract is the `callee`, and the function signature for the transfer function is `func`.

As this standard uses EIP 926, the authorisation flow is as follows:

 1. The callee contract fetches the provider for the `owner` address from the metadata registry contract, which resides at a well-known address.
 2. The callee contract calls `canCall()` with the parameters described above. If the function returns false, the callee reverts execution.

Commonly, providers will wish to supply a standardised interface for users to set and unset their own authorisations. They SHOULD implement the following interface:

```
function authoriseCaller(address owner, address caller, address callee, bytes4 func);
function revokeCaller(address owner, address caller, address callee, bytes4 func);
```

Arguments have the same meaning as in `canCall`. Implementing contracts MUST ensure that `msg.sender` is authorised to call `authoriseCaller` or `revokeCaller` on behalf of `owner`; this MUST always be true if `owner == msg.sender`. Implementing contracts SHOULD use the standard specified here to determine if other callers may provide authorisations as well.

Implementing contracts SHOULD treat a `func` of 0 as authorising calls to all functions on `callee`. If `authorised` is `false` and `func` is 0, contracts need only clear any blanket authorisation; individual authorisations may remain in effect.

## Backwards Compatibility
There are no backwards compatibility concerns.

## Implementation
Example implementation TBD.

## Copyright
Copyright and related rights waived via [CC0](https://creativecommons.org/publicdomain/zero/1.0/).