Web service like API Controller class in asp.net C#

 using System;

using System.Collections.Generic;
using System.Linq;
using System.Net;
using System.Net.Http;
using System.Web.Http;

namespace WebAPIKeyAuth.Controllers
{
    public class EmployeeController : ApiController
    {
        [HttpGet]
        [Route("api/employees")]
        public IHttpActionResult GetEmployees()
        {
            List employeeList = new List()
            {
                new Employee() {Id = 1, Name="Employee1", Designation="Manager" },
                 new Employee() {Id = 2, Name="Employee2", Designation="Supervisor" }
            };
            return Ok(employeeList);
        }
        [HttpPost]
        [Route("api/employee/add")]
        public IHttpActionResult AddEmployee([FromBody]Employee employee)
        {
            return Ok("Employee is added in the system, Employee: " + "ID: " + employee.Id.ToString() + ", Name: " + employee.Name);
        }
    }
}

reference :- https://www.codingpointer.com/asp-dot-net-tutorial/rest-web-api-key-authentication