I need to list folders using service account credentials without using the GCP Java client library. I need to call using REST API as there is restriction on making use of GCP Java client library. Is there any sample or example I can refer to make REST API calls in Java/Spring?
You can use RestTemplate and this dependency
<dependency>
<groupId>com.auth0</groupId>
<artifactId>java-jwt</artifactId>
<version>3.14.0</version>
</dependency>
Then, read your service account JSON file (here my key.json
file) and enjoy! Let me know if some part are not clear!
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"));
EDIT 1
To generate and get an ID_Token, required if you want to generate a token to call Cloud Run, Cloud Functions or App Engine deployed in secured mode. You need to replace the scope claim by the target_audience URL. And at the end, print the id_token and not the access token
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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