What are the main return types supported in ASP. Net Web API?

 It supports the following return types:

HttpResponseMessage

IHttpActionResult

Void

Other types such as string, int, etc

How to register an exception filter globally?

 One can register exception filter globally using following code:

Web API global filters are registered through the HttpConfiguration object available to you in the Register method WebApiConfig.cs if you're using a project template with WebActivator:

public static void Register(HttpConfiguration config)
{
    //stuff before
    config.Filters.Add(new MyWebApiFilter());
    //stuff after
}

or otherwise in the global.asax.cs:

GlobalConfiguration.Configuration.Filters.Add(new MyWebApiFilter());

How to handle errors in Web API?

 One can use HttpResponseException, HttpError, Exception filters, register exception filters, Exception handlers to handle errors. Exception filter can be used to identify unhandled exceptions on actions or controllers, exception handlers can be used to identify any type of unhandled exception application-wide, and HttpResponseException can be used when there is the possibility of an exception.

Explain media type formatters.

 In web API, media type formatters are classes that are responsible for serialization data.

Web API can understand request data format in a better way and send data in a format that the client expects. It simply specifies data that is being transferred among client and server in HTTP response or request. 

JsonMediaTypeFormatter ->application/json, text/json

XmlMediaTypeFormatter ->application/xml, text/json

 

What Is an Idempotent API? How to handle multiple request in web API.

Consuming ASP.NET Web API REST Service In ASP.NET MVC Using HttpClient

 Steps to Consume Web API in MVC.

Step1: Install HTTP Client library from NuGet.

What is HttpClient?

HttpClient is base class which is responsible to send HTTP request and receive HTTP response resources i.e from REST services.

Step2:Install WebAPI.Client library from NuGet

Step3: Add Model and Controller class.

Step4: 

Our hosted Web API REST Service includes these two methods, as given below.

GetAllEmployees (GET )

GetEmployeeById (POST ) which takes id as input parameter

We are going to call GetAllEmployees method which returns the all employee details ,The hosted web api REST service base URL is http://192.168.95.1:5555/ and to call GetAllEmployees from hosted web API REST service, The URL should be Base url+api+apicontroller name +web api method name as following,

http://192.168.95.1:5555/api/Employee/GetAllEmployees

In the preceding url

http://localhost:56290 Is the base address of web API service, It can be different as per your server.

api It is the used to differentiate between Web API controller and MVC controller request .

Employee This is the Web API controller name.

GetAllEmployees This is the Web API method which returns the all employee list.

using ConsumingWebAapiRESTinMVC.Models;
using Newtonsoft.Json;
using System;
using System.Collections.Generic;
using System.Net.Http;
using System.Net.Http.Headers;
using System.Threading.Tasks;
using System.Web.Mvc;

namespace ConsumingWebAapiRESTinMVC.Controllers
{
    public class HomeController : Controller
    {
        //Hosted web API REST Service base url
        string Baseurl = "http://192.168.95.1:5555/";
        public async Task<ActionResult> Index()
        {
            List<Employee> EmpInfo = new List<Employee>();
            using (var client = new HttpClient())
            {
                //Passing service base url
                client.BaseAddress = new Uri(Baseurl);
                client.DefaultRequestHeaders.Clear();
                //Define request data format
                client.DefaultRequestHeaders.Accept.Add(new MediaTypeWithQualityHeaderValue("application/json"));
                //Sending request to find web api REST service resource GetAllEmployees using HttpClient
                HttpResponseMessage Res = await client.GetAsync("api/Employee/GetAllEmployees");
                //Checking the response is successful or not which is sent using HttpClient
                if (Res.IsSuccessStatusCode)
                {
                    //Storing the response details recieved from web api
                    var EmpResponse = Res.Content.ReadAsStringAsync().Result;
                    //Deserializing the response recieved from web api and storing into the Employee list
                    EmpInfo = JsonConvert.DeserializeObject<List<Employee>>(EmpResponse);
                }
                //returning the employee list to view
                return View(EmpInfo);
            }
        }
    }
}

C#

Web API Securities JWT Token.

 What is JWT Token?

JWT stands for Jason Web Token.

Token-based security is commonly used in today’s security architecture. There are several token-based security techniques. JWT is one of the more popular techniques. JWT token is used to identify authorized users.

What is the JWT WEB TOKEN?

Open Standard: Means anywhere, anytime, and anyone can use JWT.

Secure data transfer between any two bodies, any two users, any two servers.

It is digitally signed: Information is verified and trusted.

There is no alteration of data.

Compact: because JWT can be sent via URL, post request & HTTP header.

Fast transmission makes JWT more usable.

Self Contained: because JWT itself holds user information.

It avoids querying the database more than once after a user is logged in and has been verified.

JWT is useful for:

Authentication

Secure data transfer

JWT Token Structure 

A JWT token contains a Header, a Payload, and a Signature. 

Header

Header contains the algorithms like RSA or HMACSHA256 and the information of the type of Token.

1. {  
2.    “alg” : ”” Algorithm like RSA or HMACSHA256  
3.    “Type” : ”” Type of JWT Token  
4. }  

Payload

Payload contains the information of rows, i.e., user credentials.

1. {  
2.    “loginname” : ”Gajendra”  
3.    “password”:”123#”  
4. }  

• It contains claims.
• Claims are user details or additional information

Signature

{ base64urlencoded (header) +”.”+ base64urlencoded (payload) +”.”+ secret }

• Combine base64 encoded Header , base64 encoded Payload with secret
• These provide more security.
• 
  
• A combination of all headers, payload and signatures converts into JWT TOKEN.

How Does JWT Work?

Step 1 :

 

Client logs in with his/her credentials.

Step 2:

Server generates a Jwt token at server side. 

 

Step 3 :                                                                                                                                                 

After token generation, the server returns a token in response.                                                       

Step 4:                                                                                                                               

Now, the client sends a copy of the token to validate the token. 

Step 5                                                                                                   

 

The server checks JWT token to see if it's valid or not.

Step 6 :                                                                                                                         

 After the token is validated, the server sends a status message to the client.

The server can trust the client because the JWT is signed, and there is no need to call the database to retrieve the information you already stored in the JWT.

To keep them secure, you should always store JWTs inside an httpOnly cookie. This is a special kind of cookie that’s only sent in HTTP requests to the server. It’s never accessible (both for reading or writing) from JavaScript running in the browser.

https://blog.logrocket.com/jwt-authentication-best-practices/

Steps to Implement JWT Authentication in Asp.net Core

• Understanding JWT Authentication Workflow.
• Create Asp.net Core Web API project
• Install NuGet Package (JwtBearer)
• Asp.net Core JWT appsetting.json configuration
• Asp.net Core Startup.cs - configure services add JwtBearer
• Create Models User, Tokens
• Create JWTManagerRepository to Authenticate users and generate JSON Web Token.
• Create UserController - Authenticate action method.

https://codepedia.info/jwt-authentication-in-aspnet-core-web-api-token