Google Authenticator is a free security application that generates unique codes for two-factor authentication (2FA) purposes. 2FA is an added layer of security used to verify a user's identity by requiring them to provide two pieces of evidence: something they know (such as a password) and something they have (such as a smartphone).

The Google Authenticator app generates a time-based one-time password (TOTP) valid for a short period, typically 30 seconds. This code can be used as the second factor in a 2FA setup, along with a password or other first factor.

To use Google Authenticator, you must first enable 2FA on your account or app. Then, download and install the Google Authenticator app on your smartphone or tablet. When you log in to your account or app, you will be prompted to enter the unique code generated by the app along with your password. This ensures that even if someone knows your password, they cannot log in without access to the second factor code generated by the Google Authenticator app.

Overall, 2FA adds an extra layer of security to your online accounts and helps protect you against various online attacks, such as phishing and password theft.

To implement 2-Factor Google Authenticator using Asp Net Core and Angular, you can follow the below steps,

1. Install the Google Authenticator NuGet package,
Install-Package GoogleAuthenticator

2. In the Asp Net Core application, create a class named "TwoFactorAuthenticatorService" and add the following code,
using Google.Authenticator;
using System;
using System.Collections.Generic;
using System.Linq;
using System.Threading.Tasks;

public class TwoFactorAuthenticatorService
{
    public string GenerateQrCodeUri(string email, string secretKey)
    {
        var tfa = new TwoFactorAuthenticator();
        return tfa.GenerateQrCodeUri(email, secretKey);
    }

    public bool ValidateTwoFactorPin(string secretKey, string twoFactorCode)
    {
        var tfa = new TwoFactorAuthenticator();
        return tfa.ValidateTwoFactorPIN(secretKey, twoFactorCode);
    }

    public string GenerateNewSecretKey()
    {
        var tfa = new TwoFactorAuthenticator();
        var setupCode = tfa.GenerateSetupCode("My App", "My User", "mysecretkey", 300, 300);
        return setupCode.Secret;
    }
}

3. In the Angular application, create a component named "TwoFactorAuthenticatorComponent" and add the following code,
import { Component } from '@angular/core';
import { HttpClient } from '@angular/common/http';

@Component({
  selector: 'app-two-factor-authenticator',
  templateUrl: './two-factor-authenticator.component.html',
  styleUrls: ['./two-factor-authenticator.component.css']
})
export class TwoFactorAuthenticatorComponent {
  email: string;
  secretKey: string;
  qrCode: string;
  twoFactorCode: string;

  constructor(private http: HttpClient) { }

  generateSecretKey() {
    this.http.get('/api/twofactorauthenticator/generatesecretkey').subscribe((result: any) => {
      this.secretKey = result;
      this.qrCode = 'https://chart.googleapis.com/chart?chs=300x300&chld=M|0&cht=qr&chl=' + encodeURIComponent(result);
    });
  }

  validateTwoFactorCode() {
    this.http.post('/api/twofactorauthenticator/validatetwofactorcode', { secretKey: this.secretKey, twoFactorCode: this.twoFactorCode }).subscribe((result: any) => {
      if (result) {
        alert('Valid code!');
      } else {
        alert('Invalid code!');
      }
    });
  }
}

4. In the Angular application, create a template for the "TwoFactorAuthenticatorComponent" component and add the following code,
<div>
  <label>Email:</label>
  <input type="text" [(ngModel)]="email">
</div>
<div>
  <button (click)="generateSecretKey()">Generate Secret Key</button>
</div>
<div *ngIf="secretKey">
  <img [src]="qrCode">
  <p>Secret Key: {{ secretKey }}</p>
</div>
<div>
  <label>Two Factor Code:</label>
  <input type="text" [(ngModel)]="twoFactorCode">
  <button (click)="validateTwoFactorCode()">Validate Two Factor Code</button>
</div>

5. In the Asp Net Core application, create a controller named "TwoFactorAuthenticatorController" and add the following code:
using Microsoft.AspNetCore.Mvc;
using QRCoder;
using System;
using System.Drawing;
using TwoFactorAuthenticator;

namespace YourNamespace.Controllers
{
    public class TwoFactorAuthenticatorController : Controller
    {
        // Action method to generate the QR code for the user to scan and set up their Two-Factor Authentication
        public IActionResult GenerateQRCode()
        {
            // Generate the Two-Factor Authentication secret key
            var secretKey = new Base32Encoder().Encode(Encoding.ASCII.GetBytes(Guid.NewGuid().ToString().Replace("-", "").Substring(0, 10)));

            // Generate the QR code for the user to scan
            var qrCodeGenerator = new QRCodeGenerator();
            var qrCodeData = qrCodeGenerator.CreateQrCode($"otpauth://totp/YourAppName:YourUserName?secret={secretKey}&issuer=YourAppName", QRCodeGenerator.ECCLevel.Q);
            var qrCode = new QRCode(qrCodeData);
            var qrCodeImage = qrCode.GetGraphic(20);

            // Return the QR code image to the user
            return File(qrCodeImage, "image/png");
        }

        // Action method to verify the user's Two-Factor Authentication code
        [HttpPost]
        public IActionResult VerifyCode(string code)
        {
            // Get the user's Two-Factor Authentication secret key from the database or other storage location
            var secretKey = "yourSecretKey";

            // Verify the One-Time Password (OTP) entered by the user
            var tfa = new TwoFactorAuthenticator();
            var result = tfa.ValidateTwoFactorPIN(secretKey, code);

            // If the OTP is valid, redirect the user to their account or other authorized page
            if (result)
            {
                return RedirectToAction("Index", "Home");
            }
            else
            {
                // If the OTP is invalid, return an error message to the user
                ModelState.AddModelError("code", "The code entered is invalid.");
                return View();
            }
        }
    }
}

This article discusses the implemention 2-Factor Google Authenticator using Asp Net Core and Angular in detail.

Sometimes we want to share what we are doing, the changes that we are performing, or a proof of concept with others. To do this, we need to publish our app or share the screen with others and show step-by-step what we are doing and how it works. Ngrok is an application for this scenario; it's petty simple to use and free with some limitations.

In Visual Studio 2022, we have now the possibility to share quickly our web application with a https public URL.

Since this is a preview feature in Visual Studio we need to navigate to Tools -> Manage preview features

And check the option "Enable dev tunnels for web applications"

After that in our ASP.NET core web application, we need to open launchsettings.json and add 2 properties to the general profile to include now the functionality to open the application using dev tunnels, or you can also create a new profile.

Example
"profiles": {
    "WebApplication1": {
        "commandName": "Project",
        "dotnetRunMessages": true,
        "launchBrowser": true,
        "applicationUrl": "https://localhost:7211;http://localhost:5258",
        "environmentVariables": {
            "ASPNETCORE_ENVIRONMENT": "Development"
        },
        "devTunnelEnabled": true,
        "devTunnelAccess": true
    },
    "IIS Express": {
        "commandName": "IISExpress",
        "launchBrowser": true,
        "environmentVariables": {
            "ASPNETCORE_ENVIRONMENT": "Development"
        }
    }
}

Finally, you can now run the profile changed or the new profile that includes the 2 dev tunnel properties and run the application in a public URL that other people can see.

We need to confirm that we want to use the dev tunnel in the browser

This is the website running using dev tunnels:

You can now share this site with others, every time that you can execute your project Visual Studio will generate a new URL.

Angular comes bundled with an app_initializer token, allowing developers to execute some code before the application starts running. It provides a way to load data, perform authentication, or configure the application environment before the application is rendered in the browser.

The app_initializer token is defined as a provider in the @angular/core module. It takes a function as an argument and returns a Promise or an Observable. When the application starts, Angular invokes the app_initializer provider and waits for the Promise or Observable to resolve before rendering the application.

To use app_initializer in your application, you must define a function that performs the initialization tasks and returns a Promise or Observable. For example, you want to load some configuration data before the application starts. You can define an app_initializer provider in your app.module.ts file as follows:
import { NgModule, APP_INITIALIZER } from '@angular/core';
import { AppConfigService } from './app-config.service';

export function initialize(appConfig: AppConfigService) {
  return () => appConfig.load();
}

@NgModule({
  providers: [
    AppConfigService,
    {
      provide: APP_INITIALIZER,
      useFactory: initialize,
      deps: [AppConfigService],
      multi: true
    }
  ],
  ...
})
export class AppModule { }

In the above example, we define an AppConfigService that loads configuration data from a remote server. The load method returns a Promise that resolves when the data is loaded. We are also defining an initialize function that takes the AppConfigService as a dependency and returns a function that calls the load method.

The APP_INITIALIZER provider is then defined in the providers array of the AppModule. We pass the initialize function as the useFactory parameter and specify the AppConfigService as a dependency in the deps array. We also set the multi parameter to true to allow multiple initialization functions.

With the above setup, when the application starts, Angular will invoke the initialize function and call the load method of the AppConfigService. Angular will wait for the Promise returned by the load method to resolve before rendering the application.

In conclusion, the app_initializer feature in Angular is a powerful tool that allows developers to perform initialization tasks before the application starts running. It provides a clean and efficient way to initialize your Angular application. By defining an app_initializer provider, you can execute code to load data, perform authentication, or configure the application environment.

In this article, we will learn how to create a password and confirm password matching validation in an Angular application. Password and confirm password matching validation is generally required in the registration form and password reset or create form.

Prerequisites
    Basic knowledge of Angular
    Visual Studio Code
    Node and NPM installed
    Bootstrap

For this article, I have created an Angular project using Angular 12. For creating an Angular project, we need to follow the following steps:

Create an Angular Project
Let's create a new angular project by using the following command.
ng new PassValidationExample

Open a project in Visual Studio Code using the following commands.
cd PassValidationExample
Code .

Now in Visual Studio, your project looks as below.

For validation, we need to import Validators from  '@angular/forms'
import { FormGroup, FormControl, FormBuilder, Validators } from '@angular/forms';

App.component.html
<div class="container">

    <div style="margin: 30px">
        <h1 class="ion-text-center">Register</h1>

        <form [formGroup]="loginForm">
            <div class="form-group">
                <label>First Name*</label>
                <input class="form-control" formControlName="fname" type="text" />
            </div>
            <div class="error-messages">
                <ng-container *ngFor="let error of error_messages.fname">
                    <div class="error-message" *ngIf="loginForm.get('fname').hasError(error.type) && (loginForm.get('fname').dirty || loginForm.get('fname').touched)">
                        {{ error.message }}
                    </div>
                </ng-container>
            </div>

            <div class="form-group">
                <label>Last Name*</label>
                <input class="form-control" formControlName="lname" type="text" />
            </div>
            <div class="error-messages">
                <ng-container *ngFor="let error of error_messages.lname">
                    <div class="error-message" *ngIf="loginForm.get('lname').hasError(error.type) && (loginForm.get('lname').dirty || loginForm.get('lname').touched)">
                        {{ error.message }}
                    </div>
                </ng-container>
            </div>

            <div class="form-group">
                <label>Email Id*</label>
                <input class="form-control" formControlName="email" type="text" />
            </div>
            <div class="error-messages">
                <ng-container *ngFor="let error of error_messages.email">
                    <div class="error-message" *ngIf="loginForm.get('email').hasError(error.type) &&
    (loginForm.get('email').dirty || loginForm.get('email').touched)">
                        {{ error.message }}
                    </div>
                </ng-container>
            </div>

            <div class="form-group">
                <label>Password*</label>
                <input class="form-control" formControlName="password" type="password" />
            </div>
            <div class="error-messages">
                <ng-container *ngFor="let error of error_messages.password">
                    <div class="error-message" *ngIf="loginForm.get('password').hasError(error.type) && (loginForm.get('password').dirty || loginForm.get('password').touched)">
                        {{ error.message }}
                    </div>
                </ng-container>
            </div>

            <div class="form-group">
                <label>Confirm Password*</label>
                <input class="form-control" formControlName="confirmpassword" type="password" />
            </div>
            <div class="error-messages">
                <ng-container *ngFor="let error of error_messages.confirmpassword">
                    <div class="error-message" *ngIf="loginForm.get('confirmpassword').hasError(error.type) && (loginForm.get('confirmpassword').dirty || loginForm.get('confirmpassword').touched)">
                        {{ error.message }}
                    </div>
                </ng-container>
            </div>
      <pre>
        Form Error - {{ loginForm.errors | json }}
      </pre>
            <button class="form-control btn btn-primary" [disabled]="!loginForm.valid">Signup</button>
        </form>
    </div>
</div>

App.component.ts
import { Component } from '@angular/core';
import { FormGroup, FormControl, FormBuilder, Validators } from '@angular/forms';

@Component({
  selector: 'my-app',
  templateUrl: './app.component.html',
  styleUrls: ['./app.component.css']
})
export class AppComponent {
  loginForm: FormGroup;

  error_messages = {
    'fname': [
      { type: 'required', message: 'First Name is required.' },
    ],

    'lname': [
      { type: 'required', message: 'Last Name is required.' }
    ],

    'email': [
      { type: 'required', message: 'Email is required.' },
      { type: 'minlength', message: 'Email length.' },
      { type: 'maxlength', message: 'Email length.' },
      { type: 'required', message: 'please enter a valid email address.' }
    ],

    'password': [
      { type: 'required', message: 'password is required.' },
      { type: 'minlength', message: 'password length.' },
      { type: 'maxlength', message: 'password length.' }
    ],
    'confirmpassword': [
      { type: 'required', message: 'password is required.' },
      { type: 'minlength', message: 'password length.' },
      { type: 'maxlength', message: 'password length.' }
    ],
  }

  constructor(
    public formBuilder: FormBuilder
  ) {
    this.loginForm = this.formBuilder.group({
      fname: new FormControl('', Validators.compose([
        Validators.required
      ])),
      lname: new FormControl('', Validators.compose([
        Validators.required
      ])),
      email: new FormControl('', Validators.compose([
        Validators.required,
        Validators.minLength(6),
        Validators.maxLength(30)
      ])),
      password: new FormControl('', Validators.compose([
        Validators.required,
        Validators.minLength(6),
        Validators.maxLength(30)
      ])),
      confirmpassword: new FormControl('', Validators.compose([
        Validators.required,
        Validators.minLength(6),
        Validators.maxLength(30)
      ])),
    }, {
      validators: this.password.bind(this)
    });
  }

  ngOnInit() {
  }

  password(formGroup: FormGroup) {
    const { value: password } = formGroup.get('password');
    const { value: confirmPassword } = formGroup.get('confirmpassword');
    return password === confirmPassword ? null : { passwordNotMatch: true };
  }

}

App.component.css
p {
  font-family: Lato;
}
.error-message {
  color: red;
}
input.ng-touched.ng-invalid {
  border: 1px solid red;
}

Now run the project using the following command
npm start

In this article, I have discussed the implementation of password and confirm password matching validation in Angular application.

.NET Core and Node.js are two popular technologies for building APIs (Application Programming Interfaces). Both have their strengths and weaknesses, and the choice between them depends on the specific requirements of a project.

.NET Core is a cross-platform, open-source framework for building modern applications. It is developed by Microsoft and is part of the .NET ecosystem. .NET Core is based on C#, a statically-typed language. It supports LINQ (Language Integrated Query) and Entity Framework, making it easier to query data. .NET Core also provides a strong security model, built-in support for WebSockets, and the ability to run on Windows, Linux, and macOS.

Node.js, on the other hand, is an open-source, cross-platform JavaScript runtime environment. It is event-driven and non-blocking, making it highly efficient for real-time applications. Node.js has a vast and growing ecosystem, with numerous packages and tools available for a variety of purposes, including building APIs.

When it comes to building APIs, .NET Core is a good choice if you're looking for a framework with a strong security model, good performance, and the ability to handle large amounts of data. .NET Core is also a good choice if you're already familiar with C# and the .NET ecosystem, as this will reduce the learning curve.

Node.js, on the other hand, is a good choice if you're looking for a fast and efficient API that can handle real-time data and can be scaled horizontally. Node.js is also a good choice if you're already familiar with JavaScript and the Node.js ecosystem, as this will reduce the learning curve.

Similarities between .Net Core and Node
Despite their differences, .NET Core and Node.js have some similarities as well. Here are some of the most notable similarities between the two technologies:

Cross-platform compatibility
Both .NET Core and Node.js are cross-platform technologies, which means that they can run on multiple operating systems, including Windows, Linux, and macOS.

Open-source
Both .NET Core and Node.js are open-source technologies, which means that their source code is available for anyone to use, modify, or contribute to.

Large and active communities
Both .NET Core and Node.js have large and active communities of developers, which means that there is a wealth of knowledge, tools, and resources available for these technologies.

Fast and efficient
Both .NET Core and Node.js are designed to be fast and efficient, making them well-suited for building high-performance applications, including APIs.

Support for modern web technologies
Both .NET Core and Node.js support modern web technologies, such as REST and WebSockets, making it easy to build modern, scalable APIs.

Difference between .Net Core and Node
While .NET Core and Node.js have some similarities, they also have some notable differences that make them well-suited for different types of projects. Here are some of the most important differences between the two technologies,

Language
.NET Core is based on C#, a statically-typed language, while Node.js is based on JavaScript, a dynamically-typed language. This can impact the development experience and the performance of the resulting application.

Performance
.NET Core is generally considered to be a more performant framework, especially for applications that require handling large amounts of data. Node.js, on the other hand, is designed for real-time, event-driven applications and is highly efficient for these types of applications.

Ecosystem
.NET Core is part of the .NET ecosystem, which includes a large number of libraries, tools, and frameworks for building applications. Node.js has a growing and vibrant ecosystem of its own, with a large number of packages and tools available for a wide range of purposes.

Security
.NET Core provides a strong security model, with built-in support for authentication, authorization, and encryption. Node.js, while secure, does not provide the same level of security features out-of-the-box as .NET Core.

Scalability
Node.js is designed to be highly scalable, with the ability to run multiple instances of the application on multiple machines to handle increased traffic. .NET Core also supports scalability, but it may require additional work to achieve the same level of scalability as Node.js.

.NET Core and Node.js are both powerful technologies for building APIs, but they have some important differences that make them well-suited for different types of projects. The choice between the two will depend on the specific requirements of a project, including the desired performance, security, scalability, and skills of the development team.

In conclusion, despite the differences between .NET Core and Node.js, the two technologies have some similarities, including cross-platform compatibility, open-source nature, large and active communities, fast and efficient performance, and support for modern web technologies.

Conclusion
In conclusion, the choice between .NET Core and Node.js depends on the specific requirements of a project. .NET Core is a good choice for projects that require a strong security model and good performance, while Node.js is a good choice for projects that require real-time data and scalability. Before making a choice, it is important to consider the specific requirements of a project and the skills of the development team.

Thanks for reading my article.

In this article, we will discuss two important decorators that we use to send data from one component to another or send data from child to parent component or vice-versa.

For a better understanding, we take one example: we will send data from the parent component to the child component using the input decorator and then send data from the child component to the parent component using the output decorator.

Let’s start with the input decorator
@Input

Input decorator is used to send data from parent to child component.

Let’s start with a practical demo
    First, create an angular application and one child component inside the newly created application.
    Import input decorator from the angular core package.
    Next, add one property with some messages which need to pass the child component.

import { Component } from '@angular/core';

@Component({
    selector: 'app-root',
    templateUrl: './app.component.html',
    styleUrls: ['./app.component.css']
})
export class AppComponent {
    title = 'demo';
    parentMessage: string = "Hello from parent component..";
}

After that, add the same property to the child component selector.
<nav class="navbar navbar-light bg-light" style="padding: 30px;margin: 40px; justify-content:center">
  <span class="navbar-brand mb-0 h1">Angular Component Communication</span>
</nav>

<app-child [parentMessageData]="parentMessage"></app-child>
<div class="divider"><div>

Here, we pass the newly created property by the parent app component inside the child component selector and the syntax is like first need to mention the child component property in the square bracket which gets the data, and in double quote parent component property.

After that, inside the child component, we just receive that message using the input decorator as shown in below and display the same inside the child template.
import { Component, EventEmitter, Input, Output } from '@angular/core';

@Component({
    selector: 'app-child',
    templateUrl: './child.component.html',
    styleUrls: ['./child.component.css']
})
export class ChildComponent {
    @Input() parentMessageData: string = "";
}

Finally, display the message by parent inside the template using string interpolation
<div class="alert alert-secondary" role="alert" style="padding: 30px;margin: 40px;">
    <h3>Child Component</h3>
    <h5>{{parentMessageData}}</h5>
</div>

The output decorator is used to send data from the child component to the parent component.

Component Communication in Angular
The property with output decorator is initialized with an event emitter that flows event data from the child to the parent component.
The type of output decorator should be an event emitter and here we pass a string with an event emitter which indicates the event is stored string type of data.
import { Component, EventEmitter, Input, Output } from '@angular/core';
@Component({
    selector: 'app-child',
    templateUrl: './child.component.html',
    styleUrls: ['./child.component.css']
})
export class ChildComponent {
    @Output() childMessage: EventEmitter < string > = new EventEmitter < string > ();
    dataHandler() {
        this.childMessage.emit("Hello from child component....")
    }
}

The child component raises an event so the parent component knows some things are changed by a child component and received the event.

For the output decorator, first, we create one button inside the child component and that will create one event and one handler function to emit that event.
<div class="alert alert-secondary" role="alert" style="padding: 30px;margin: 40px;">
    <h3>Child Component</h3>
    <button (click)="dataHandler()">Send Data To Parent Component</button>
</div>

After that, in the parent component template and inside the child component selector we bind the parent method with the child component event.
<nav class="navbar navbar-light bg-light" style="padding: 30px;margin: 40px; justify-content:center">
  <span class="navbar-brand mb-0 h1">Angular Component Communication</span>
</nav>
<div class="alert alert-primary" role="alert" style="padding: 30px;margin: 40px;">
  <h3>Parent Component:</h3>
  <h5>{{childMessage}}</h5>
</div>
<app-child (childMessage)="GetMessage($event)"></app-child>
<div class="divider"><div>

Next, create one function which handles the event and store them inside a new property in the parent component.
import { Component } from '@angular/core';

@Component({
    selector: 'app-root',
    templateUrl: './app.component.html',
    styleUrls: ['./app.component.css']
})
export class AppComponent {
    title = 'demo';
    childMessage: string = "";
    GetMessage(res: any) {
        this.childMessage = res;
    }
}

Basically, the child component notifies the parent component about the newly generated event.

Let’s run the application,

Here as we can see in the above image, the message is displayed inside the child component section which is sent by the parent with the help of the input decorator.
Below the message, there is one button that generates one event and in the TS file, the event emitter emits the same and sends a notification to the parent and after that, the event message is displayed in the parent component section as shown in the below image.

This is all about input and output decorators.

In this article, I will introduce how to download a file in Angular with a button click and show an example. For this article, I have created an Angular project using Angular 12. For creating an Angular project, we need to follow the following steps:

Create an Angular Project
Let's create a new angular project by using the following command.
ng new fileDownloadExample

Open a project in Visual Studio Code using the following commands.
cd fileDownloadExample
Code .

Now in Visual Studio, your project looks as below.

App.Component.html
<a [href]="fileUrl" download="file.txt">DownloadFile</a>

App.Component.ts
import { Component, OnInit } from '@angular/core';
import { DomSanitizer } from '@angular/platform-browser';

@Component({
    selector: 'my-app',
    templateUrl: './app.component.html',
    styleUrls: ['./app.component.css']
})
export class AppComponent implements OnInit {
    name = 'Angular 5';
    fileUrl;
    constructor(private sanitizer: DomSanitizer) {}
    ngOnInit() {
        const data = 'some text';
        const blob = new Blob([data], {
            type: 'application/octet-stream'
        });
        this.fileUrl = this.sanitizer.bypassSecurityTrustResourceUrl(window.URL.createObjectURL(blob));
    }
}

Now Run the project using the following command
npm start

and click on the link and you will see the downloaded file