Unable to connect to the remote server System.Net.Sockets.SocketException: An attempt was made to access a socket in a way forbidden by its access permissions

Discussed in https://github.com/pnp/pnpframework/discussions/482

^{Originally posted by vivekagrawal1110 October 5, 2021}
I have ASP.Net Web API, to perform SharePoint operation using SharePoint add-in client context . I have deployed Web API on Azure Web Site.
Generally API works fine but randomly gives exception till that Web Site restarts manually.

System.Net.WebException: Unable to connect to the remote server System.Net.Sockets.SocketException: An attempt was made to access a socket in a way forbidden by its access permissions 20.190.151.68:443 at System-NetSockets.Socket.DoConnect(EndPoint endPointSnapshot, SocketAddress socketAddress) at System.Net.ServicePoint.ConnectSocketlnternal(Boolean connectFailure, Socket s4, Socket s6, Socket& socket, IPAddress& address, ConnectSocketState state, IAsyncResult asyncResult, Exception& exception) End of inner exception stack trace at System.Net.WebClient.DownloadDatalnternal(Uri address, WebRequest& request) at System.Net.WebClient.DownloadData(Uri address) at System.Net.WebClient.DownloadData(String address) at PnP.Framework.Utilities.TokenHelper GetMetadataDocument(String realm) at PnP.Framework.Utilities.TokenHelper.GetStsUrl(String realm) at PnP.Framework.Utilities.TokenHelper.GetAppOnlyAccessToken(String targetPrincipalName, String targetHost, String targetRealm) at PnRFramework.LJtilities.ACSTokenGenerator.GetToken(lJri siteurl) at PnP.Framework.AuthenticationManager.b_56_0(String site) at PnP.Framework.AuthenticationManager. DisplayClass68_0.b 0(Object sender, WebRequestEventArgs args) at Microsoft.SharePoint.Client.CIientRuntimeContext.OnExecutingWebRequest(WebRequestEventArgs args) at Microsoft.SharePoint.Client.ClientContext.GetWebRequestExecutor() at Microsoft.SharePoint Client ClientContext.GetFormDigestI nfoPrivate() at Microsoft.SharePoint.Client ClientContext.EnsureFormDigest() at Microsoft.SharePoint.Client.ClientContext.ExecuteQuery()

Please help me to fix this issue.

Start with the stack-trace entry points TokenHelper.GetMetadataDocument, TokenHelper.GetStsUrl, AuthenticationManager, and ClientContext.ExecuteQuery. Reproduce the intermittent Azure Web API failure and determine the conditions behind the socket access error; done means the cause is documented and the failure is addressed or clearly bounded.