Generalised authorisations
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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 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:
- The callee contract fetches the provider for the
owner
address from the metadata registry contract, which resides at a well-known address. - 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.