Check For Updates" does not work under the authentication proxy

In my company, we must access Web sites on the Internet via authentication proxy server which adopts BASIC authentication. When calling "git clone" via HTTPS from GitHub, we experience no problem and proxy authentication works normally, however, in case if we click on "Check For Updates", we encounter below error messages saying proxy authentication is required. As a result, we are unable to update our Source Tree. ERROR [2019-04-10 11:21:20,371] [1] [Sourcetree.Installer.Squirrel.Utils.UpdateHelper] [Log] - Couldn't read staging user ID ERROR [2019-04-10 11:21:20,376] [1] [Sourcetree.Installer.Squirrel.Utils.UpdateHelper] [Log] - Couldn't read staging user ID ERROR [2019-04-10 11:21:24,662] [1] [Sourcetree.Installer.Squirrel.Utils.UpdateHelper] [Log] - Unable to check for Updates. System.Net.WebException: The remote server returned an error: (407) Proxy authentication required at System.Net.HttpWebRequest.EndGetResponse(IAsyncResult asyncResult) at System.Net.WebClient.GetWebResponse(WebRequest request, IAsyncResult result) at System.Net.WebClient.DownloadBitsResponseCallback(IAsyncResult result) — End of stack trace from previous location where exception was thrown — at System.Runtime.ExceptionServices.ExceptionDispatchInfo.Throw() at System.Runtime.CompilerServices.TaskAwaiter.HandleNonSuccessAndDebuggerNotification(Task task) at Squirrel.Utility.<LogIfThrows>d__43`1.MoveNext() — End of stack trace from previous location where exception was thrown — at System.Runtime.ExceptionServices.ExceptionDispatchInfo.Throw() at System.Runtime.CompilerServices.TaskAwaiter.HandleNonSuccessAndDebuggerNotification(Task task) at Squirrel.FileDownloader.<DownloadUrl>d__3.MoveNext() — End of stack trace from previous location where exception was thrown — at System.Runtime.ExceptionServices.ExceptionDispatchInfo.Throw() at System.Runtime.CompilerServices.TaskAwaiter.HandleNonSuccessAndDebuggerNotification(Task task) at Squirrel.UpdateManager.CheckForUpdateImpl.<CheckForUpdate>d__2.MoveNext() — End of stack trace from previous location where exception was thrown — at System.Runtime.ExceptionServices.ExceptionDispatchInfo.Throw() at System.Runtime.CompilerServices.TaskAwaiter.HandleNonSuccessAndDebuggerNotification(Task task) at Squirrel.UpdateManager.<CheckForUpdate>d__7.MoveNext() — End of stack trace from previous location where exception was thrown — at System.Runtime.ExceptionServices.ExceptionDispatchInfo.Throw() at System.Runtime.CompilerServices.TaskAwaiter.HandleNonSuccessAndDebuggerNotification(Task task) at Sourcetree.Installer.Squirrel.Utils.UpdateHelper.<CheckForUpdate>d__16.MoveNext() — End of stack trace from previous location where exception was thrown — at System.Runtime.ExceptionServices.ExceptionDispatchInfo.Throw() at System.Runtime.CompilerServices.TaskAwaiter.HandleNonSuccessAndDebuggerNotification(Task task) at Sourcetree.Installer.Squirrel.Utils.UpdateHelper.<HasAvailableUpdates>d__17.MoveNext()