var provider = new FileExtensionContentTypeProvider();      
provider.Mappings.Add(".apk", "application/vnd.android.package-archive");      
app.UseStaticFiles(new StaticFileOptions      
{        
    ContentTypeProvider = provider,
    FileProvider = new Microsoft.Extensions.FileProviders.PhysicalFileProvider(System.IO.Directory.GetCurrentDirectory() + @"/App"),
    RequestPath = $ "/项目名称/App" // 存放APP的文件夹   
});