google http load balancing - 返回401 Unauthorized

Question

我有一个HTTP负载均衡器设置，如下所示。内容将根据URL路由到后端存储桶或实例组。

防火墙允许端口80上的所有内容

当我尝试使用负载均衡IP访问API时，出现错误Status Code: 401 Unauthorized。

以下是该特定请求的Stackdriver日志记录快照。

    http://3xxxxxx5/api/GetAccountTransaction?key=AIzaSyC3xxxxxxMHNAxKM
     1xxxxxx06 - "POST http://3xxxxxx5/api/GetAccountTransaction?key=AIzaSyC3xxxxxxMHNAxKM" 401 494 "http://3xxxxxx5/" "Mozilla/5.0 (Windows NT 6.1; Win64; x64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/65.0.3325.181 Safari/537.36"
    Expand all | Collapse all {
     httpRequest: {
      referer:  "http://3xxxxxx5/"   
      remoteIp:  "1xxxxxx06"   
      requestMethod:  "POST"   
      requestSize:  "559"   
      requestUrl:  "http://3xxxxxx5/api/GetAccountTransaction?key=AIzaSyC3xxxxxxMHNAxKM"   
      responseSize:  "494"   
      status:  401   
      userAgent:  "Mozilla/5.0 (Windows NT 6.1; Win64; x64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/65.0.3325.181 Safari/537.36"   
     }
     insertId:  "efo39lf8k5sux"  
     jsonPayload: {
      @type:  "type.googleapis.com/google.cloud.loadbalancing.type.LoadBalancerLogEntry"   
      statusDetails:  "response_sent_by_backend"   
     }
     logName:  "projects/sixxxxxx4204/logs/requests"  
     receiveTimestamp:  "2018-03-30T12:09:37.539673973Z"  
     resource: {
      labels: {
       backend_service_name:  ""    
       forwarding_rule_name:  "prepay-ip-address"    
       project_id:  "sixxxxxx4204"    
       target_proxy_name:  "prepay-service-target-proxy"    
       u

rl_map_name:  "prepay-service"    
   zone:  "global"    
  }
  type:  "http_load_balancer"   
 }
 severity:  "WARNING"  
 spanId:  "5da2dc551e28dbcc"  
 timestamp:  "2018-03-30T12:09:36.491864533Z"  
 trace:  "projects/sixxxxxx4204/traces/52617f14af59859ee38e759f605bc545"  
}

但是，当我使用相同的请求但使用VM实例的外部IP时，它可以工作。

负载均衡器的此错误引用了什么身份验证？