How can I send push notifications using FCM HTTP v1 with OAuth2 authorization?

When migrating to the HTTP v1 API, there are two major changes you need to account for:

1. Authorization
   Instead of using a static server key, you must generate a short‑lived OAuth 2.0 access token from your service account credentials (or use Application Default Credentials). This token is then sent in the header as:
   "Authorization": "Bearer ACCESS_TOKEN"
   where ACCESS_TOKEN is a valid OAuth 2.0 token. An API key (or any other static string) will not work with the HTTP v1 endpoint.

2. Message Payload Structure
   The payload format is different. In the legacy API you were using the registration_ids field; however, with v1 the payload needs to be nested under a "message" key and you must use the field "token" (or "topic"/"condition") to target devices. For example, a message to a single device should be structured as:

   JAVASCRIPTCopied
   async function sendPushNotification(deviceToken) {
     // You need to generate a valid OAuth2 access token from your service account credentials
     const ACCESS_TOKEN = await getAccessToken(); // Implement this using your preferred method
   
     const message = {
       message: {
         token: deviceToken, // Use "token" for a single device. HTTP v1 does not support "registration_ids".
         notification: {
           title: "Title Here",
           body: "Your account has been verified."
         },
         android: {
           priority: "high",
           // You can add other Android-specific options here.
         },
         // Optionally, add platform-specific overrides (e.g., apns, webpush) here.
       }
     };
   
     const response = await fetch(
       "https://fcm.googleapis.com/v1/projects/YOUR_PROJECT_ID/messages:send",
       {
         method: "POST",
         headers: {
           "Content-Type": "application/json",
           Authorization: "Bearer " + ACCESS_TOKEN,
         },
         body: JSON.stringify(message),
       }
     );
   
     const data = await response.json();
     console.log("Response:", data);
   }

   Key points:

   • Replace YOUR_PROJECT_ID with your actual Firebase project ID.
   • Replace the function getAccessToken() with your implementation to obtain an OAuth2 token using your service account credentials. For server environments (like Cloud Functions, App Engine, or Compute Engine), you can often use Application Default Credentials (ADC).
   • For sending to multiple devices, note that the HTTP v1 API does not support a registration_ids array. You’d need to send separate messages (or use topics if the use case fits).

By ensuring you:

• Use a valid OAuth 2.0 access token (instead of a static API key)
• Construct the message payload according to the HTTP v1 spec (nesting the payload under a "message" key and using "token" for targeting)

you should be able to successfully send push notifications using FCM HTTP v1.