How do I add an ethereum wallet address to my next.id DID?

[javaspeak]

The docs:

https://docs.next.id/rest-api/proofservice-platforms-supported

have the following text on an adding an ethereum id to your next.id DID:

platform	identity	proof_location
ethereum	Wallet address 0x123AbC...	N/A

My question is:

1. How do I create a two-way signature?
2. Can the two-way signature be created with viem library?
3. what does the post look like with these 2 signatures?

[javaspeak]

POST: https://proof-service.nextnext.id/v1/proof

Payload:

{
    "action": "create",
    "platform": "ethereum",
    "identity": "0x8dd1Cc73D574608BA7E27C485dA4E3645C62FBf6",
    "public_key": "0x046ca64e70760e7635e10161095693abb08e9548ff84bed952fc08ce3ccc196736383d1673f699625e78080b9072d433bbac69e8f81d3430d9746615b69d9e9924",
    "extra": {
        "wallet_signature": "gQWh59jDC/ryj1F9+2mV8oMk1n5sPfsab0E3G0v4EWcGacZmuIymDtEm6dn6OupjLChSKBAY5EsGAU0qK96e4Rw=",
        "signature": "gQWh59jDC/ryj1F9+2mV8oMk1n5sPfsab0E3G0v4EWcGacZmuIymDtEm6dn6OupjLChSKBAY5EsGAU0qK96e4Rw="
    },
    "uuid": "7b6b7d3f-5004-4469-b727-42ddd1f3a46f",
    "created_at": "1705862170"
}

Response: 201 Created

{}

Note that one of the signatures is from the wallet that created the avatar. And the other is the signature from the wallet address that we want added to the avatar.

In our case they are the same wallet address.

[javaspeak]

When dealing with wallets one would need to connect to:

(i) the wallet the avatar was created with to be able to sign payload data
(ii) connect to the wallet which has the address we want to add to the avatar and sign payload data

This means both wallet addressed neet to be in metamask.

So one way of doing this in the wallet world is to:

(i) Prompt the user to connect to their avatar wallet address
(ii) Get the payload to sign
(iii) Sign it and get the signature
(iv) Save the signature and payload we signed in storage
(v) Connect to the wallet address we want to add to our avatar
(vi) Sign the payload
(vii) Save the signature in storage
(viii) Connect back to the wallet address which made the avatar
(ix) Dig out both signatures from storage and send the proof
(x) Delete Signatures from storage

This is not that easy for end users. They need to be careful about which address they are connecting to.

Of course no storage and switching between addresses is required if both addresses are the same one. The addresses are the same if we want to add the same address which made the avatar to the avatar.