FCM Authorization always fails - google-cloud-messaging

Question

Today i wanted to switch from GCM to FCM so i set up everything needed and wanted to implement the server side code. I used the gcm4j library and changed it so that the adress goes to https://fcm.googleapis.com/fcm/send.
So im doing the following:
FCM fcm = new FCMDefault(new FCMConfig().withKey(FCMGlobals.FCM_API_KEY));
FCMRequest request = new FCMRequest().withRegistrationId(android.getRegistration())
// .withCollapseKey(collapseKey)
.withDelayWhileIdle(true)
.withDataItem(FCMGlobals.FCM_PARAM_CODE, code)
.withDataItem(FCMGlobals.FCM_PARAM_USER_ID, "" + user.getId())
.withDataItem(FCMGlobals.FCM_PARAM_ADDITION, "" + addition);
ListenableFuture<FCMResponse> responseFuture = fcm.send(request);
Futures.addCallback(responseFuture, new FutureCallback<FCMResponse>() {
public void onFailure(Throwable t) {
log.error(t);
}
#Override
public void onSuccess(FCMResponse response) {
log.info(response.toString());
}
});
The implementation for that is:
protected FCMResponse executeRequest(FCMRequest request) throws IOException {
byte[] content = this.objectMapper.writeValueAsBytes(request);
HttpURLConnection conn = this.connectionFactory.open(this.fcmUrl);
conn.setRequestMethod("POST");
conn.addRequestProperty("Authorization", getAuthorization(request));
conn.addRequestProperty("Content-Type", "application/json");
conn.setDoOutput(true);
conn.setFixedLengthStreamingMode(content.length);
LoggerFactory.getLogger("FCMDefaultAbstract").info("Authorization: " + conn.getRequestProperty("Authorization"));
LoggerFactory.getLogger("FCMDefaultAbstract").info("Content-Type: " + conn.getRequestProperty("Content-Type"));
LoggerFactory.getLogger("FCMDefaultAbstract").info("send: " + new String(content));
try (OutputStream outputStream = conn.getOutputStream()) {
IOUtils.write(content, outputStream);
} catch (Exception e) {
throw new FCMNetworkException("Error sending HTTP request to FCM", e);
}
FCMResponse response;
try (InputStream inputStream = conn.getInputStream()) {
response = this.objectMapper.readValue(IOUtils.toByteArray(inputStream), FCMResponse.class);
} catch (IOException e) {
try (InputStream inputStreamError = conn.getErrorStream()) {
String str = inputStreamError != null ? IOUtils.toString(inputStreamError) : "No error details provided";
int responseCode = conn.getResponseCode();
if (responseCode < 500) {
throw new FCMNetworkException(conn.getResponseCode(), str.trim(), e);
} else {
throw new FCMNetworkException(conn.getResponseCode(), str.trim(), checkForRetryInResponse(conn), e);
}
}
}
response.setRequest(request);
response.setRetryAfter(checkForRetryInResponse(conn));
Iterator<String> iteratorId = request.getRegistrationIds().iterator();
Iterator<FCMResult> iteratorResponse = response.getResults().iterator();
while (iteratorId.hasNext() && iteratorResponse.hasNext()) {
iteratorResponse.next().setRequestedRegistrationId(iteratorId.next());
}
if (iteratorId.hasNext()) {
LOG.warn("Protocol error: Less results than requested registation IDs");
}
if (iteratorResponse.hasNext()) {
LOG.warn("Protocol error: More results than requested registation IDs");
}
return response;
}
Here the log output:
FCMDefaultAbstract Authorization: null
FCMDefaultAbstract Content-Type:application/json
FCMDefaultAbstract send: {"registration_ids":["dMpvzp*************************************2lRsSl_5lFET2"],"data":{"CODE":"201","USER_ID":"1","ADDITION":"1468083549493"},"delay_while_idle":true}
FCM FCMNetworkException: HTTP 401: No error details provided
The Authorization header is not null in fact. it is correctly set with my FCM API Key. Only the HTTPUrlConnection implementation says to return null if someone trys to access Authorization key.
As you can see i am not able to connect with FCM. The Code 401 means that authentication failed.
What could be the problem here?

Answer 1

Check that you are using a server type API-KEY, and not a client or browser API-KEY.
If you are using Firebase you can find the API-KEY in
Project Settings > Cloud Messaging
If you are using cloud console, or you are not sure which key you are using,
you can generate a new key through through https://console.cloud.google.com
Quoting the documentation
https://firebase.google.com/docs/cloud-messaging/concept-options#credentials
Server key: A server key that authorizes your app server for access to
Google services, including sending messages via Firebase Cloud
Messaging. [...]
Important: Do not include the server key anywhere in your client code.
Also, make sure to use only server keys to authorize your app server.
Android, iOS, and browser keys are rejected by FCM.