Use a simple check to verify proxies during registration.

libsignal/service/src/main/java/org/whispersystems/signalservice/api/SignalServiceAccountManager.java

@@ -632,6 +632,10 @@ public class SignalServiceAccountManager {
     return this.pushServiceSocket.getTurnServerInfo();
   }
 
+  public void checkNetworkConnection() throws IOException {
+    this.pushServiceSocket.pingStorageService();
+  }
+
   /**
    * @return The avatar URL path, if one was written.
    */

libsignal/service/src/main/java/org/whispersystems/signalservice/internal/push/PushServiceSocket.java

@@ -885,6 +885,10 @@ public class PushServiceSocket {
     }
   }
 
+  public void pingStorageService() throws IOException {
+    makeStorageRequest(null, "/ping", "GET", null);
+  }
+
   public RemoteConfigResponse getRemoteConfig() throws IOException {
     String response = makeServiceRequest("/v1/config", "GET", null);
     return JsonUtil.fromJson(response, RemoteConfigResponse.class);