Firestore Messaging: Sending message to Topic with Swift

Question

I'm converting my iOS app over from CloudKit to Firestore. So far everything is working great except for notifications. I have users subscribed to specific topics which works great if I use the website to send a message.

However, I need my iOS app to send a message and google provides amazing documentation on how to do that. Their instructions are

(Send to a single Topic)
POST https://fcm.googleapis.com/v1/projects/myproject-b5ae1/messages:send HTTP/1.1

Content-Type: application/json
Authorization: Bearer (Server Key)
{
  "message":{
    "topic" : "foo-bar",
    "notification" : {
      "body" : "This is a Firebase Cloud Messaging Topic Message!",
      "title" : "FCM Message"
      }
   }
}

So in order to do that, I decided to use an http request to post that information. Here's my code...

let json: [String: Any] = ["message": ["topic":"\(Items.sharedInstance.clubSelected2.id)", "notification":["body":"Test Body","title":"Test Title"]]]
let jsonData = try? JSONSerialization.data(withJSONObject: json)

let url = URL(string: "https://fcm.googleapis.com/v1/projects/(My Project)/messages:send")!
var request = URLRequest(url: url)

request.setValue("application/json", forHTTPHeaderField: "Content-Type")
request.setValue("Bearer (My Server Key)", forHTTPHeaderField: "Authorization")
request.httpMethod = "POST"
request.httpBody = jsonData

let task = URLSession.shared.dataTask(with: request) { data, response, error in
    guard let data = data, error == nil else {
        // check for fundamental networking error
        print("error=\(error)")
        return
    }

    if let httpStatus = response as? HTTPURLResponse, httpStatus.statusCode != 200 {           // check for http errors
        print("statusCode should be 200, but is \(httpStatus.statusCode)")
        print("response = \(response)")
    }

    let responseString = String(data: data, encoding: .utf8)
        print("responseString = \(responseString)")
    }
    task.resume()

With all of this, I get the error "Request had invalid authentication credentials. Expected OAuth 2 access token, login cookie or other valid authentication credential. See https://developers.google.com/identity/sign-in/web/devconsole-project .\\". I have created new server keys and still get the same error. The following is what I have tried for the Authorization field... without the parenthesis of course

• Bearer (Server Key)
• Bearer (New Server Key)
• Bearer (Legacy Server Key)
• key=(Server Key)
• key=(New Server Key)
• key=(Legacy Server Key)

Any help in what could fix this authorization error would be greatly appreciated!

Answer 1

FCM v1 does not send messages from the client, only from a server. You need to use XMPP to send outgoing messages directly from the client. Personally, I'd prefer to send from a server. You could send an outgoing request to your server to handle the message, or trigger a Cloud Function to run automatically.

If you want to use FCM v1, the latest version of FCM, you'll need to send from a server instead. Firebase offers Admin SDKs , which enable you to access Firebase products server-side. Then you don't have to handle generating credentials or building the request.

When using the FCM v1 endpoint through a POST request instead of through the Admin SDK, credentials for FCM v1 are generated using the Service Account Key JSON file. See instructions in the guide . You can download the file from the Firebase console here . Select your project to go to the location in the dashboard. Included in the guide is the code for getting the credentials from the file.