JAVA怎么使用MetaMask作OAuth认证登陆

最近开发DAPP项目需要使用以太坊账号，与微信／QQ／微博等OAuth认证登陆类似。

老外写的这个认证流程不错，流程与代码都非常清晰，使用node.js实现

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One-Click Login with Blockchain: a MetaMask Tutorial
github：https://github.com/amaurymartiny/login-with-metamask-demo

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认证流程

• Step 1: Modify the User Model (Back-end)
• Step 2: Generate Nonces (Back-end)
• Step 3: User Fetches Their Nonce (Front-end)
• Step 4: User Signs the Nonce (Front-end)
• Step 5: Signature Verification (Back-end)
• Step 6: Change the Nonce (Back-end)

image

因为项目后端为java开发，这里使用Java来对签名消息做认证。

• Injected web3(Metamask web3js)

这里主要讲下后端Step 5: Signature Verification，其他步骤都比较简单

后端使用

• Spring MVC
• web3j(https://github.com/web3j/web3j)

集成web3j

web3j提供了springboot的集成方式，https://github.com/web3j/web3j-spring-boot-starter

<dependency>
    <groupId>org.web3j</groupId>
    <artifactId>web3j-spring-boot-starter</artifactId>
    <version>1.6.0</version>
</dependency>

签名消息认证工具

本文最重要的部分，也是作者参考资料文献尝试了好多遍之后的成果，任何消息处理的步骤不对都会导致认证失败。

package com.bc.utils;

import org.web3j.crypto.*;
import org.web3j.utils.Numeric;
import org.web3j.crypto.Sign.SignatureData;

import java.math.BigInteger;
import java.util.Arrays;

/**
 * 以太坊签名消息校验工具
 */
public class CryptoUtils {
    /**
     * 以太坊自定义的签名消息都以以下字符开头
     * 参考 eth_sign in https://github.com/ethereum/wiki/wiki/JSON-RPC
     */
    public static final String PERSONAL_MESSAGE_PREFIX = "\u0019Ethereum Signed Message:\n";

    /**
     * 对签名消息，原始消息，账号地址三项信息进行认证，判断签名是否有效
     *
     * @param signature
     * @param message
     * @param address
     * @return
     */
    public static boolean validate(String signature, String message, String address) {
        //参考 eth_sign in https://github.com/ethereum/wiki/wiki/JSON-RPC
        // eth_sign
        // The sign method calculates an Ethereum specific signature with:
        //    sign(keccak256("\x19Ethereum Signed Message:\n" + len(message) + message))).
        //
        // By adding a prefix to the message makes the calculated signature recognisable as an Ethereum specific signature.
        // This prevents misuse where a malicious DApp can sign arbitrary data (e.g. transaction) and use the signature to
        // impersonate the victim.
        String prefix = PERSONAL_MESSAGE_PREFIX + message.length();
        byte[] msgHash = Hash.sha3((prefix + message).getBytes());

        byte[] signatureBytes = Numeric.hexStringToByteArray(signature);
        byte v = signatureBytes[64];
        if (v < 27) {
            v += 27;
        }

        SignatureData sd = new SignatureData(
                v,
                Arrays.copyOfRange(signatureBytes, 0, 32),
                Arrays.copyOfRange(signatureBytes, 32, 64));

        String addressRecovered = null;
        boolean match = false;

        // Iterate for each possible key to recover
        for (int i = 0; i < 4; i++) {
            BigInteger publicKey = Sign.recoverFromSignature(
                    (byte) i,
                    new ECDSASignature(new BigInteger(1, sd.getR()), new BigInteger(1, sd.getS())),
                    msgHash);

            if (publicKey != null) {
                addressRecovered = "0x" + Keys.getAddress(publicKey);

                if (addressRecovered.equals(address)) {
                    match = true;
                    break;
                }
            }
        }
        return match;
    }
}

Controller样例

import org.web3j.crypto.WalletUtils;
import com.bc.utils.CryptoUtils;

    @RequestMapping(value = "/oauth/metamask", method = RequestMethod.POST)
    @ResponseBody
    public ResponseMessage login(@RequestBody HashMap requestObject) throws InterruptedException {
        final String publicAddress = (String) requestObject.get("publicAddress");
        final String signature = (String) requestObject.get("signature");
        final String message = (String) requestObject.get("message");
        
        // 地址合法性校验
        if (!WalletUtils.isValidAddress(publicAddress)) {
            // 不合法直接返回错误
            return Result.error("地址格式非法！");
        }

        // 校验签名信息
        if (!CryptoUtils.validate(signature, message, publicAddress)) {
            return Result.error("签名校验失败！");
        }
        
        // 校验通过，publicAddress 相当于就是OAuth的openid, 根据该账号做其他业务处理
        ...
        // 
        // JWT token
        ...
    }

大功告成！

其他问题

正式环境使用小狐狸的话还要考虑以下几点：

• 小狐狸是否连接到了你想要的区块链网络
• 页面侦测小狐狸的账号切换，切换之后应用作相应处理