feat: add spotify resolver

src/examples/SpotifyResolver.sol

@@ -0,0 +1,50 @@
+// SPDX-License-Identifier: Unlicensed
+pragma solidity ^0.8.24;
+
+import {INebulaResolver} from "../INebulaResolver.sol";
+
+contract SpotifyResolver is INebulaResolver {
+    address owner;
+
+    constructor() {
+        owner = msg.sender;
+    }
+
+    // keccak256 hash of zero bytes
+    bytes32 ZERO_BYTES_KECCAK =
+        0xc5d2460186f7233c927e7db2dcc703c0e500b653ca82273b7bfad8045d85a470;
+
+    mapping(address => bytes) userVerificationData;
+
+    // data will contain signature (r, s, v) and hashed data
+    function issue(
+        address recipient,
+        bytes calldata data
+    ) external returns (bool) {
+        bytes32 hash;
+        bytes32 r;
+        bytes32 s;
+        uint8 v;
+        (hash, r, s, v) = abi.decode(data, (bytes32, bytes32, bytes32, uint8));
+        address signer = ecrecover(hash, v, r, s);
+        if (signer != owner) return false;
+        userVerificationData[recipient] = data;
+        return true;
+    }
+
+    function verify(
+        address recipient,
+        bytes calldata /*data*/
+    ) external view returns (bool) {
+        if (keccak256(userVerificationData[recipient]) == ZERO_BYTES_KECCAK)
+            return false;
+        return true;
+    }
+
+    function revoke(
+        address /*recipient*/,
+        bytes calldata /*data*/
+    ) external pure returns (bool) {
+        return false;
+    }
+}