Call public method

 public class ConfigModel : PageModel
    {
        private IConfiguration _configuration;
        public ConfigModel(IConfiguration iconfig)
        {
            _configuration = iconfig;
        }

        public string UserName
        {
            get
            {
                return _configuration.GetValue<string>("Data:UserName");
            }
            set { }
        }

 public class TestClass
    {
        private static IConfiguration _configuration;
        public static ConfigModel Config = new ConfigModel(_configuration);
        public void ExampleLogin()
        {
            var a = Config.UserName;
            var b = Config.Password;

            
        }
        }