Swift中FCM从Legacy API迁移至HTTP V1的Bearer令牌获取问题

FCM HTTP V1要求使用OAuth2 Bearer令牌（有效期1小时），推荐缓存令牌，过期后再重新获取，不用每次发送都请求。以下是两种可行实现方案：

方式一：使用Google官方Auth库（推荐，简化实现） #

1. 添加依赖：通过Swift Package Manager引入google-auth-library-swift，依赖地址：https://github.com/googleapis/google-auth-library-swift
2. 令牌获取逻辑：

import GoogleAuthLibrary

// 加载从Google云控制台下载的服务账号JSON密钥文件
guard let serviceAccountPath = Bundle.main.path(forResource: "service-account", ofType: "json"),
      let credentials = ServiceAccountCredentials(fromFile: serviceAccountPath) else {
    print("加载服务账号密钥失败")
    return
}

// 指定FCM权限范围
let scopes = ["https://www.googleapis.com/auth/firebase.messaging"]

// 内部自动缓存令牌，过期自动刷新
credentials.getToken(withScopes: scopes) { result in
    switch result {
    case .success(let token):
        let bearerToken = token.accessToken
        self.sendFCMV1Push(to: "用户设备令牌", title: "推送标题", body: "推送内容", bearerToken: bearerToken)
    case .failure(let error):
        print("获取令牌失败：\(error.localizedDescription)")
    }
}

3. 修正FCM V1推送请求格式（你原代码参数为Legacy格式，需调整）：

func sendFCMV1Push(to token: String, title: String, body: String, bearerToken: String) {
    // 补全HTTPS前缀
    let urlString = "https://fcm.googleapis.com/v1/projects/myproject-77a88/messages:send"
    guard let url = URL(string: urlString) else {
        print("无效的推送URL")
        return
    }
    
    // FCM V1标准请求格式
    let paramString: [String: Any] = [
        "message": [
            "token": token,
            "notification": [
                "title": title,
                "body": body,
                "badge": "1",
                "sound": "default"
            ]
        ]
    ]
    
    var request = URLRequest(url: url)
    request.httpMethod = "POST"
    request.httpBody = try? JSONSerialization.data(withJSONObject: paramString)
    request.setValue("application/json", forHTTPHeaderField: "Content-Type")
    request.setValue("Bearer \(bearerToken)", forHTTPHeaderField: "Authorization")
    
    let task = URLSession.shared.dataTask(with: request) { data, response, error in
        if let error = error {
            print("推送请求失败：\(error.localizedDescription)")
            return
        }
        do {
            if let jsonData = data,
               let jsonDict = try JSONSerialization.jsonObject(with: jsonData) as? [String: Any] {
                print("推送响应：\(jsonDict)")
            }
        } catch {
            print("响应解析失败：\(error.localizedDescription)")
        }
    }
    task.resume()
}

方式二：手动生成JWT并请求令牌（无第三方依赖，轻量场景） #

如果不想引入库，可以手动生成JWT并调用Google OAuth2接口获取令牌：

1. 生成JWT（需引入轻量库SwiftJWT处理RSA签名）：

import SwiftJWT

// 定义Google OAuth2所需的JWT声明结构
struct GoogleClaims: Claims {
    let iss: String // 服务账号的client_email
    let scope: String // FCM权限范围：https://www.googleapis.com/auth/firebase.messaging
    let aud: String // 固定值：https://oauth2.googleapis.com/token
    let exp: Date // 过期时间，建议设为当前时间+3600秒（1小时）
    let iat: Date // 签发时间
}

func generateJWT() -> String? {
    let serviceAccountEmail = "your-service-account@myproject-77a88.iam.gserviceaccount.com"
    let privateKey = "-----BEGIN PRIVATE KEY-----\n你的服务账号私钥内容\n-----END PRIVATE KEY-----"
    
    let claims = GoogleClaims(
        iss: serviceAccountEmail,
        scope: "https://www.googleapis.com/auth/firebase.messaging",
        aud: "https://oauth2.googleapis.com/token",
        exp: Date().addingTimeInterval(3600),
        iat: Date()
    )
    
    var jwt = JWT(claims: claims)
    guard let privateKeyData = privateKey.data(using: .utf8),
          let signer = try? JWTSigner.rs256(privateKey: privateKeyData) else {
        return nil
    }
    return try? jwt.sign(using: signer)
}

2. 请求Bearer令牌：

func fetchBearerToken(completion: @escaping (String?) -> Void) {
    guard let jwt = generateJWT() else {
        completion(nil)
        return
    }
    
    let urlString = "https://oauth2.googleapis.com/token"
    guard let url = URL(string: urlString) else {
        completion(nil)
        return
    }
    
    let params = [
        "grant_type": "urn:ietf:params:oauth:grant-type:jwt-bearer",
        "assertion": jwt
    ]
    
    var request = URLRequest(url: url)
    request.httpMethod = "POST"
    request.httpBody = params.map { "\($0.key)=\($0.value.addingPercentEncoding(withAllowedCharacters: .urlQueryAllowed)!)" }.joined(separator: "&").data(using: .utf8)
    request.setValue("application/x-www-form-urlencoded", forHTTPHeaderField: "Content-Type")
    
    let task = URLSession.shared.dataTask(with: request) { data, response, error in
        if let error = error {
            print("获取令牌失败：\(error.localizedDescription)")
            completion(nil)
            return
        }
        do {
            if let jsonData = data,
               let jsonDict = try JSONSerialization.jsonObject(with: jsonData) as? [String: Any],
               let accessToken = jsonDict["access_token"] as? String {
                completion(accessToken)
            } else {
                completion(nil)
            }
        } catch {
            print("令牌响应解析失败：\(error.localizedDescription)")
            completion(nil)
        }
    }
    task.resume()
}

// 使用示例
fetchBearerToken { token in
    if let bearerToken = token {
        self.sendFCMV1Push(to: "用户设备令牌", title: "标题", body: "内容", bearerToken: bearerToken)
    }
}

注意事项 #

• 令牌有效期1小时，建议缓存令牌，每次发送前检查是否过期，过期再重新获取，避免频繁请求令牌接口
• 原代码中URL缺少https://前缀，必须补上否则请求会失败
• FCM V1的请求参数必须包裹在message字段下，目标设备令牌用token字段而非Legacy版的to

内容的提问来源于stack exchange，提问作者Christine