我正试图用下面的代码打谷歌分析API。getAccessToken（）;返回null：

@RequestMapping(value = "/process", method = RequestMethod.POST, consumes = "text/plain")
    public ResponseEntity<String> process(@RequestBody String payload) throws Exception {
        GoogleCredentials credentials = GoogleCredentials.fromStream(new FileInputStream("C:\\Firm_Initiatve\\workspace-spring-tool-suite-4-4.8.1.RELEASE\\googleAnalyticsRest\\src\\main\\resources\\flowing-sign-294117-8998a8e44928.json"));
          if (credentials.createScopedRequired()) { 
              credentials = credentials.createScoped(Collections.singletonList("https://www.googleapis.com/auth/analytics")); 
              }
        credentials.refreshIfExpired();
        AccessToken token = credentials.getAccessToken();
        HttpHeaders headers = new HttpHeaders();
        headers.set("Authorization", token.toString());
        headers.setContentType(MediaType.APPLICATION_JSON);
        RestTemplate restTemplate = new RestTemplate();
        HttpEntity<String> request = new HttpEntity<String>(payload, headers);
        String personResultAsJsonString = restTemplate.postForObject(appURL, request, String.class);
        return new ResponseEntity<String>(personResultAsJsonString, HttpStatus.OK);

字符串

但它的错误与下面的错误：

java.io.IOException: Error getting access token for service account: 400 Bad Request
POST https://oauth2.googleapis.com/token
{"error":"invalid_grant","error_description":"Invalid JWT Signature."}
    at com.google.auth.oauth2.ServiceAccountCredentials.refreshAccessToken(ServiceAccountCredentials.java:444) ~[google-auth-library-oauth2-http-0.22.1.jar:na]
    at com.google.auth.oauth2.OAuth2Credentials.refresh(OAuth2Credentials.java:157) ~[google-auth-library-oauth2-http-0.22.1.jar:na]
    at com.google.auth.oauth2.OAuth2Credentials.refreshIfExpired(OAuth2Credentials.java:174) ~[google-auth-library-oauth2-http-0.22.1.jar:na]
    at com.example.demo.AnalyticsControllerOauth.process(AnalyticsControllerOauth.java:32) ~[classes/:na]
    at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method) ~[na:1.8.0_271]

型