FCM Firebase V1 Example With PHP Backend

fcm-v1.php

<?php

function getAccessToken($serviceAccountPath) {
    $now = time();
    $payload = [
        "iss" => $serviceAccountPath['client_email'],
        "sub" => $serviceAccountPath['client_email'],
        "aud" => "https://oauth2.googleapis.com/token",
        "iat" => $now,
        "exp" => $now + 3600,
        "scope" => "https://www.googleapis.com/auth/firebase.messaging"
    ];
    
    $jwt = jwt_encode($payload, $serviceAccountPath['private_key'], 'sha256');

    $ch = curl_init();
    curl_setopt($ch, CURLOPT_URL, "https://oauth2.googleapis.com/token");
    curl_setopt($ch, CURLOPT_POST, true);
    curl_setopt($ch, CURLOPT_RETURNTRANSFER, true);
    curl_setopt($ch, CURLOPT_HTTPHEADER, ["Content-Type: application/x-www-form-urlencoded"]);
    curl_setopt($ch, CURLOPT_POSTFIELDS, http_build_query([
        "grant_type" => "urn:ietf:params:oauth:grant-type:jwt-bearer",
        "assertion" => $jwt
    ]));

    $response = curl_exec($ch);
    curl_close($ch);

    $tokenInfo = json_decode($response, true);
    return $tokenInfo['access_token'];
}

function jwt_encode($payload, $privateKey, $algo) {
    $header = json_encode(["alg" => 'RS256', "typ" => "JWT"]);
    $segments = [];
    $segments[] = rtrim(strtr(base64_encode($header), '+/', '-_'), '=');
    $segments[] = rtrim(strtr(base64_encode(json_encode($payload)), '+/', '-_'), '=');
    $signingInput = implode('.', $segments);
    $signature = sign($signingInput, $privateKey, $algo);
    $segments[] = rtrim(strtr(base64_encode($signature), '+/', '-_'), '=');
    return implode('.', $segments);
}

function sign($data, $key, $algo) {
    openssl_sign($data, $signature, $key, $algo);
    return $signature;
}

function sendFCMNotification($accessToken, $projectId, $message) {
    $url = "https://fcm.googleapis.com/v1/projects/$projectId/messages:send";

    $headers = [
        "Authorization: Bearer $accessToken",
        "Content-Type: application/json"
    ];

    $ch = curl_init();
    curl_setopt($ch, CURLOPT_URL, $url);
    curl_setopt($ch, CURLOPT_POST, true);
    curl_setopt($ch, CURLOPT_RETURNTRANSFER, true);
    curl_setopt($ch, CURLOPT_HTTPHEADER, $headers);
    curl_setopt($ch, CURLOPT_POSTFIELDS, json_encode(["message" => $message]));

    $response = curl_exec($ch);
    curl_close($ch);

    return json_decode($response, true);
}

$credential = '{
    "type": "service_account",
    "project_id": "xxx",
    "private_key_id": "xxx",
    "private_key": "-----BEGIN PRIVATE KEY-----\nxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx\n-----END PRIVATE KEY-----\n",
    "client_email": "xxx",
    "client_id": "xxx",
    "auth_uri": "https://accounts.google.com/o/oauth2/auth",
    "token_uri": "https://oauth2.googleapis.com/token",
    "auth_provider_x509_cert_url": "https://www.googleapis.com/oauth2/v1/certs",
    "client_x509_cert_url": "https://www.googleapis.com/robot/v1/metadata/x509/xxxxx",
    "universe_domain": "googleapis.com"
  }';

// Example usage
$serviceAccountPath = json_decode($credential, true);
$accessToken = getAccessToken($serviceAccountPath);
$projectId = $serviceAccountPath['project_id'];
$message = [
    "token" => "fzyUqeOlR8-3xnIPlzZYD9:APA91bFbpj_B0XWTm08uzdscvYOVCrZ_4e60eOMOxN_G0WoFX3JveG1d5ZaZ2H_rB69TL4vP99IL2la6amjPDZM2fY474sAzoXMFi908VsLevsVoccueis8wrM_1wRTnsYiEyuFxMdAk",
    "notification" => [
        "title" => "Hello",
        "body" => "World"
    ]
];

$response = sendFCMNotification($accessToken, $projectId, $message);
print_r($response);

?>