如何从Java中的Apple公钥JSON响应中获取公钥？

我们正在尝试在 iOS 应用程序中添加“使用 Apple 登录”。当客户端工作正常时，我们的后端是用 Java 编写的，我们无法解码 Apple 的公钥。当您点击网址时https://appleid.apple.com/auth/keys https://appleid.apple.com/auth/keys它给你公钥。但是当我尝试做一个PublicKey对象是 Java 它不识别n and e价值从那里。这些是 Base64 编码的吗？

当我尝试解码时n and e它给我的 Base64 值illegal character 2d。我怀疑它是 base64 的原因是在 NodeJS 包中（https://www.npmjs.com/package/node-rsa https://www.npmjs.com/package/node-rsa）他们通过 base64 解码 n 和 e 值。但问题是指数值（e）是AQAB它永远不可能是base64。我如何从中创建一个 PublicKey 对象？

我正在使用的代码是：

HttpResponse<String> responsePublicKeyApple =  Unirest.get("https://appleid.apple.com/auth/keys").asString();

ApplePublicKeyResponse applePublicKeyResponse = new Gson().fromJson(responsePublicKeyApple.getBody(),ApplePublicKeyResponse.class);

System.out.println("N: "+applePublicKeyResponse.getKeys().get(0).getN());
System.out.println("E: "+applePublicKeyResponse.getKeys().get(0).getE());

byte[] decodedBytesE = Base64.getDecoder().decode(applePublicKeyResponse.getKeys().get(0).getE());
String decodedE = new String(decodedBytesE);

System.out.println("decode E: "+decodedE);

byte[] decodedBytesN = Base64.getDecoder().decode(applePublicKeyResponse.getKeys().get(0).getN());
String decodedN = new String(decodedBytesN);

System.out.println("decode N: "+decodedN);

BigInteger bigIntegerN = new BigInteger(decodedN,16);
BigInteger bigIntegerE = new BigInteger(decodedE,16);

RSAPublicKeySpec publicKeySpec = new RSAPublicKeySpec(bigIntegerN,bigIntegerE);
KeyFactory keyFactory = KeyFactory.getInstance(SignatureAlgorithm.RS256.getValue());
PublicKey publicKey = keyFactory.generatePublic(publicKeySpec);

解码部分失败n and e价值。另一件事是苹果回应称他们使用了RS256算法来签署令牌，但是当我尝试这样做时

KeyFactory keyFactory = KeyFactory.getInstance(SignatureAlgorithm.RS256.getValue());

it says RS256 keyfactory is not available.

我该如何解决这两个问题？请帮忙。

其实那些N and E值使用编码Base64 网址 https://www.rfc-editor.org/rfc/rfc4648#page-7如中所解释的RFC7518 https://www.rfc-editor.org/rfc/rfc7518#page-30。此代码将向您展示如何执行您的请求。我使用 Jackson 来读取您提供的 JSON：

String json = Files.lines(Paths.get("src/main/resources/test.json")).collect(Collectors.joining());
ObjectMapper objectMapper = new ObjectMapper();
objectMapper.configure(DeserializationFeature.FAIL_ON_UNKNOWN_PROPERTIES, false);

// here is the parsing of PublicKey
ApplePublicKeyResponse applePublicKeyResponse = objectMapper.readValue(json, ApplePublicKeyResponse.class);
        
Key key = applePublicKeyResponse.getKeys().get(0);

byte[] nBytes = Base64.getUrlDecoder().decode(key.getN());
byte[] eBytes = Base64.getUrlDecoder().decode(key.getE());

BigInteger n = new BigInteger(1, nBytes);
BigInteger e = new BigInteger(1, eBytes);

RSAPublicKeySpec publicKeySpec = new RSAPublicKeySpec(n,e);
KeyFactory keyFactory = KeyFactory.getInstance(key.getKty()); //kty will be "RSA"
PublicKey publicKey = keyFactory.generatePublic(publicKeySpec);

还如所指出的key.getKty()将返回"RSA"。所以你应该将此值传递给KeyFactory.getInstance因为你想解析 RSA 密钥并且RS256是使用 RSA 和 SHA-256 哈希的签名算法的名称。

我使用了构造函数BigInteger https://docs.oracle.com/javase/8/docs/api/java/math/BigInteger.html#BigInteger-int-byte:A-它需要符号和原始字节。 Signum 设置为 1 以获得正值。