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.
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.
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);
owneris the owner of the resource. If approved the function call is treated as being made by this address.
calleris the address making the present call.
calleeis the address of the contract being called.
funcis 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
As this standard uses EIP 926, the authorisation flow is as follows:
- The callee contract fetches the provider for the
owneraddress 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
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
func is 0, contracts need only clear any blanket authorisation; individual authorisations may remain in effect.
There are no backwards compatibility concerns.
Example implementation TBD.
Copyright and related rights waived via CC0.
Please cite this document as:
Nick Johnson, "EIP-927: Generalised authorisations [DRAFT]," Ethereum Improvement Proposals, no. 927, March 2018. [Online serial]. Available: https://eips.ethereum.org/EIPS/eip-927.