ethr DID Resolver

This library is intended to use ethereum addresses or secp256k1 publicKeys as fully self-managed
Decentralized Identifiers and wrap them in a
DID Document

It supports the proposed Decentralized Identifiers spec from the
W3C Credentials Community Group.

It requires the did-resolver library, which is the primary interface for resolving DIDs.

This DID method relies on the ethr-did-registry.

DID method

To encode a DID for an Ethereum address on the ethereum mainnet, simply prepend did:ethr:

eg:

did:ethr:0xf3beac30c498d9e26865f34fcaa57dbb935b0d74

Multi-network DIDs are also supported, if the proper configuration is provided during setup.

For example:
did:ethr:0x5:0xf3beac30c498d9e26865f34fcaa57dbb935b0d74 gets resolved on the goerli testnet (chainID=0x5), and
represents a distinct identifier than the generic one, with different DID documents and different key rotation history.

DID Document

The did resolver takes the ethereum address, looks at contract events and builds a DID document based on the ERC1056
Events corresponding to the address. When an identifier is a full publicKey, the corresponding ethereumAddress is
computed and checked in the same manner.

The minimal DID document for an ethereum address 0xb9c5714089478a327f09197987f16f9e5d936e8a with no transactions to
the registry looks like this:

``json
{
"@context": [
"https://www.w3.org/ns/did/v1",
"https://w3id.org/security/suites/secp256k1recovery-2020/v2"
],
"id": "did:ethr:0xb9c5714089478a327f09197987f16f9e5d936e8a",
"verificationMethod": [
{
"id": "did:ethr:0xb9c5714089478a327f09197987f16f9e5d936e8a#controller",
"type": "EcdsaSecp256k1RecoveryMethod2020",
"controller": "did:ethr:0xb9c5714089478a327f09197987f16f9e5d936e8a",
"blockchainAccountId": "eip155:1:0xb9c5714089478a327f09197987f16f9e5d936e8a"
}
],
"authentication": [
"did:ethr:0xb9c5714089478a327f09197987f16f9e5d936e8a#controller"
],
"assertionMethod": [
"did:ethr:0xb9c5714089478a327f09197987f16f9e5d936e8a#controller"
]
}
`

Note this resolver uses the EcdsaSecp256k1RecoveryMethod2020 type and an blockchainAccountId to represent the
default
verificationMethod, assertionMethod, and authentication entry. Any value from the registry that returns an
ethereum address will be added to the verificationMethod array of the DID document with
type EcdsaSecp256k1RecoveryMethod2020 and an blockchainAccountId attribute containing the address.

Building a DID document

The DID document is not stored as a file, but is built by using read only functions and contract events on
the ethr-did-registry Ethereum smart contract.

Please see the spec for details of how the DID document and corresponding metadata are
computed.

Resolving a DID document

The library presents a resolve() function that returns a Promise returning the DID document. It is not meant to be
used directly but through the did-resolver aggregator.

You can use the getResolver(config) method to produce an entry that can be used with the Resolver
constructor:

`javascript
import { Resolver } from 'did-resolver'
import { getResolver } from 'ethr-did-resolver'

// While experimenting, you can set a rpc endpoint to be used by the web3 provider
// You can also set the address for your own ethr-did-registry contract
const providerConfig = { rpcUrl: 'http://localhost:7545', registry: registry.address }
// It's recommended to use the multi-network configuration when using this in production
// since that allows you to resolve on multiple public and private networks at the same time.

// getResolver will return an object with a key/value pair of { "ethr": resolver } where resolver is a function used by the generic did resolver.
const ethrDidResolver = getResolver(providerConfig)
const didResolver = new Resolver(ethrDidResolver)

didResolver.resolve('did:ethr:0xf3beac30c498d9e26865f34fcaa57dbb935b0d74').then((doc) => console.log)

// You can also use ES7 async/await syntax
const doc = await didResolver.resolve('did:ethr:0xf3beac30c498d9e26865f34fcaa57dbb935b0d74')
`

Multi-network configuration

In production, you will most likely want the ability to resolve DIDs that are based in different ethereum networks. To
do this, you need a configuration that sets the network name or chain ID (and even the registry address) for each
network. An example configuration for multi-network DID resolving would look like this:

`javascript
const providerConfig = {
networks: [
{ name: "mainnet", provider: web3.currentProvider },
{ name: "0x5", rpcUrl: "https://goerli.infura.io/v3/" },
{ name: "rsk:testnet", chainId: "0x1f", rpcUrl: "https://did.testnet.rsk.co:4444" },
{ name: "development", rpcUrl: "http://localhost:7545", registry: "0xdca7ef03e98e0dc2b855be647c39abe984fcf21b" },
{ name: "myprivatenet", chainId: 123456, rpcUrl: "https://my.private.net.json.rpc.url" }
]
}

const ethrDidResolver = getResolver(providerConfig)
`

The configuration from above allows you to resolve ethr-did's of the following formats:

- did:ethr:mainnet:0xabcabc03e98e0dc2b855be647c39abe984193675
- did:ethr:0xabcabc03e98e0dc2b855be647c39abe984193675 (defaults to mainnet configuration)
- did:ethr:0x5:0xabcabc03e98e0dc2b855be647c39abe984193675 (refer to the goerli network by chainID)
- did:ethr:rsk:testnet:0xabcabc03e98e0dc2b855be647c39abe984193675
- did:ethr:0x1f:0xabcabc03e98e0dc2b855be647c39abe984193675 (refer to the rsk:testnet by chainID)
- did:ethr:development:0xabcabc03e98e0dc2b855be647c39abe984193675
- did:ethr:myprivatenet:0xabcabc03e98e0dc2b855be647c39abe984193675
- did:ethr:0x1e240:0xabcabc03e98e0dc2b855be647c39abe984193675 (refer to myprivatenet by chainID)

For each network you can specify either an rpcUrl, a provider or a web3 instance that can be used to access that
particular network. At least one of name or chainId must be specified per network.

These providers will have to support eth_call and eth_getLogs to be able to resolve DIDs specific to that network.

You can also override the default registry address by specifying a registry` attribute per network.