I have a web application running on Sharepoint Foundation 2013, but some days ago, it sometimes asked for user login when user reload page or redirect to another page.
please help, thanks.
user must login once, do not ask again when user working on it.
You can try turning on anonymous access. Users can access SharePoint content without validating their credentials. Anonymous authentication is disabled by default. You typically use anonymous authentication when you use SharePoint Server to publish content that doesn't require security and is available for all users, such as a public Internet website.
Reference: Manage anonymous access for a web application in SharePoint Server
How to Enable Anonymous Access in SharePoint 2013 / 2016