如何使用 JAVA 使用 REST API 从服务帐户凭据创建访问令牌？

你可以使用 RestTemplate 和这个依赖

        <dependency>
            <groupId>com.auth0</groupId>
            <artifactId>java-jwt</artifactId>
            <version>3.14.0</version>
        </dependency>
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然后，阅读您的服务帐户 JSON 文件（这里是我的 key.json 文件）并享受！如果某些部分不清楚，请告诉我！

        InputStream resource = new ClassPathresource("key.json").geTinputStream();

        BufferedReader reader = new BufferedReader(new InputStreamReader(resourcE));
        String keyFileJson = reader.lines().collect(Collectors.joining("\n"));
        Map keyFile = new ObjectMapper().readValue(keyFileJson,Map.class);


        String privKeyPEM = keyFile.get("private_key").toString().replace("-----BEGIN PRIVATE KEY-----","")
                .replace("-----END PRIVATE KEY-----","")
                .replaceAll("\n","");

        byte [] encoded = Base64.decode(privKeyPEM);

        PKCS8EncodedKeySpec keySpec = new PKCS8EncodedKeySpec(encoded);
        KeyFactory kf = KeyFactory.geTinstance("RSA");
        PrivateKey privKey = kf.generatePrivate(keySpec);

        String tokenUrl = "https://oauth2.googleapis.com/token";

        long now = System.currentTimeMillis();
        Algorithm algorithm = Algorithm.RSA256(null,(RSAPrivateKey)privKey);
        String signedJwt = JWT.create()
                .withKeyId(keyFile.get("private_key_id").toString())
                .withIssuer(keyFile.get("client_email").toString())
                .withAudience(tokenUrl)
                .withClaim("scope","openid https://www.googleapis.com/auth/userinfo.email https://www.googleapis.com/auth/cloud-platform https://www.googleapis.com/auth/appENGIne.admin https://www.googleapis.com/auth/compute")
                .withIssuedAt(new Date(now))
                .withExpiresAt(new Date(now + 3600 * 1000L))
                .sign(algorithm);
//        System.out.println(signedJwt);


        RestTemplate restTemplate = new RestTemplate();
        httpHeaders headers = new httpHeaders();
        headers.setContentType(MediaType.APPLICATION_FORM_URLENCODED);

        MultiValueMap<String,String> map = new LinkedMultiValueMap<>();
        map.add("assertion",signedJwt);
        map.add("grant_type","urn:ietf:params:oauth:grant-type:jwt-bearer");

        httpEntity<MultiValueMap<String,String>> entity = new httpEntity<>(map,headers);
        ResponseEntity<String> responseEntity = restTemplate.postForEntity(tokenUrl,entity,String.class);
        Map result = new ObjectMapper().readValue(responseEntity.getBody(),Map.class);
        System.out.println(result.get("access_token"));
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编辑 1
要生成并获取 ID_Token，如果您想生成令牌以调用以安全模式部署的 Cloud Run、Cloud Functions 或 App ENGIne，则需要此令牌。您需要用 target_audience URL 替换范围声明。最后，打印 id_token 而不是访问令牌
        String signedJwt = JWT.create()
                .withKeyId(keyFile.get("private_key_id").toString())
                .withIssuer(keyFile.get("client_email").toString())
                .withAudience(tokenUrl)
                .withClaim("target_audience","https://target-log-fqffbf2xsq-uc.a.run.app")
                .withIssuedAt(new Date(now))
                .withExpiresAt(new Date(now + 3600 * 1000L))
                .sign(algorithm);

...
...
...
System.out.println(result.get("id_token"));
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