如何计算服务帐户的 OAuth 签名？

Question

我想使用 HTTP/REST 方法 get a service account access token 获取 Google API，但 OAuth 向我发送了签名错误。我正在使用 Java.

我收到以下 JSON 字符串：

{
    "error": "invalid_grant",
    "error_description": "Invalid JWT Signature."
}

据我所知，在文档中，我需要使用 header、声明集和签名来编写 JWT（JSON Web 令牌）。我设法获得了正确的 header 和声明集，但显然，我的签名计算不正确。

我的进口：

import java.security.KeyFactory;
import java.security.Signature;
import java.security.spec.PKCS8EncodedKeySpec;
import java.util.Base64;
import java.security.KeyPair;
import java.security.KeyPairGenerator;
import java.security.SecureRandom;
import java.security.Security;
import java.security.PrivateKey;

这里是header计算：

String header = "{\"alg\":\"RS256\",\"typ\":\"JWT\"}";
byte[] bytes = header.getBytes();
header = Base64.getEncoder().encodeToString(bytes);

我的声明集：

long time_milis = System.currentTimeMillis()/1000L;
String claim_set = "{\n"
     + "  \"iss\":\"something@something.iam.gserviceaccount.com\",\n"
     + "  \"scope\":\"https://www.googleapis.com/auth/devstorage.read_write\",\n"
     + "  \"aud\":\"https://www.googleapis.com/oauth2/v4/token\",\n"
     + "  \"exp\":" + (time_milis + 300) + ",\n"
     + "  \"iat\":" + time_milis + "\n"
     + "}";
bytes = claim_set.getBytes();
claim_set = Base64.getEncoder().encodeToString(bytes);

为我的签名尝试做好准备！（出于明显的安全原因，我屏蔽了私钥）：

String signature = header + "." + claim_set;
String privateKeyString = "-----BEGIN PRIVATE KEY-----\nturlututu123\n-----END PRIVATE KEY-----\n";
privateKeyString = private_key.replaceAll("-----END PRIVATE KEY-----", "").replaceAll("-----BEGIN PRIVATE KEY-----", "").replaceAll("\n", "");

Signature privateSignature = Signature.getInstance("SHA256withRSA");

KeyFactory keyFactory=KeyFactory.getInstance("RSA");

PrivateKey privateKey = keyFactory.generatePrivate(
    new PKCS8EncodedKeySpec(
        Base64.getDecoder().decode(privateKeyString)
    )
);

privateSignature.initSign(privateKey);

privateSignature.update(signature.getBytes("UTF-8"));
bytes = privateSignature.sign();
signature = Base64.getEncoder().encodeToString(bytes);

我在 https://www.googleapis.com/oauth2/v4/token 以 POST 模式发送我的请求 header :

"Host: www.googleapis.com
Content-Type: application/x-www-form-urlencoded"

并在 body 中：

"grant_type=urn:ietf:params:oauth:grant-type:jwt-bearer&assertion=" + header + "." + claim_set + "." + signature

我真的卡住了，不知道如何前进。

Answer 1

终于找到答案了！这是一个编码问题。事实上，当我对字符串进行编码时，我调用了 Base64.getEncoder() 编码器而不是 Base64.getUrlEncoder() 编码器。现在我们可以更改所有脚本了。

这里是header计算：

String header = "{\"alg\":\"RS256\",\"typ\":\"JWT\"}";
byte[] bytes = header.getBytes();
header = Base64.getUrlEncoder().encodeToString(bytes);

我的声明集：

long time_milis = System.currentTimeMillis()/1000L;
String claim_set = "{\n"
     + "  \"iss\":\"something@something.iam.gserviceaccount.com\",\n"
     + "  \"scope\":\"https://www.googleapis.com/auth/devstorage.read_write\",\n"
     + "  \"aud\":\"https://www.googleapis.com/oauth2/v4/token\",\n"
     + "  \"exp\":" + (time_milis + 300) + ",\n"
     + "  \"iat\":" + time_milis + "\n"
     + "}";
bytes = claim_set.getBytes();
claim_set = Base64.getUrlEncoder().encodeToString(bytes);

和签名（出于明显的安全原因，我屏蔽了私钥）：

String signature = header + "." + claim_set;
String privateKeyString = "-----BEGIN PRIVATE KEY-----\nturlututu123\n-----END PRIVATE KEY-----\n";
privateKeyString = private_key.replaceAll("-----END PRIVATE KEY-----", "").replaceAll("-----BEGIN PRIVATE KEY-----", "").replaceAll("\n", "");

Signature privateSignature = Signature.getInstance("SHA256withRSA");

KeyFactory keyFactory=KeyFactory.getInstance("RSA");

PrivateKey privateKey = keyFactory.generatePrivate(
    new PKCS8EncodedKeySpec(
        Base64.getDecoder().decode(privateKeyString)
    )
);

privateSignature.initSign(privateKey);

privateSignature.update(signature.getBytes("UTF-8"));
bytes = privateSignature.sign();
signature = Base64.getUrlEncoder().encodeToString(bytes);

感谢 this post 在调试过程中帮助了我。

如何计算服务帐户的 OAuth 签名？

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