WEBVTT

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Hi everyone.

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Let's go to with the.

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NestJS fundamental and core concept of NestJS.

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Okay this here will be guard.

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This is very important concept inside NestJS.

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And the guard is also the class.

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And this will be a dependency injection class which implement the something called CanActive interface.

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Now you can see the guard right here.

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Okay.

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It will protect the route handler.

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Let me let me show you something like this, actually the guard.

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We have a single responsibility okay.

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This will determine the request will be handled by router or not okay.

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This is the whole purpose of the guard.

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And we usually use in the authorization.

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Okay.

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Now we if you already know the express.js, in the NestJS  sorry, in the express.js, we normally

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use the middleware to handle the authentication or authorization.

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Right?

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But NestJS we will use the guard because it will follow the single responsibility concept one class only.

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Only responsible for one purpose, and the purpose of the guard

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It will handle it will determine okay the route handler.

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Now you can see, you can read more about the detail inside the document, it say the middleware, by

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the nature, it's dump.

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Okay.

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Very fun.

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Right?

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And with middleware, it doesn't know the which.

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It means let me summarize.

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When we call the next function in the middleware, it doesn't know okay.

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It doesn't know which handler will be executed

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Okay.

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After we go to next it doesn't know anything.

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But with the guard it has an execution context.

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Okay.

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It means it's more powerful than the middleware a little bit.

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Now that enough.

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Let me show you how we can create a guard inside the NestJS.

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Inside the guard, right

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Here I will create one more folder call guards

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And again, you don't need to remember that code

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Okay.

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This is just the common code from Nestjs.

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And it's already provided by documentation.

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You doesn't know.

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Doesn't need to know what's in the code.

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Okay, let me copy everything over here.

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And I will create auth.guard.ts and paste everything right here.

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And now it have a validate request.

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Right now I will return true

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Now you can see it will return a boolean or promise.

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Boolean.

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Uh.

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Observable.

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Boolean.

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And the reason because promise Boolean right here, it can be used by async function.

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Right.

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For example if this is an async function.

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Sorry for that.

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Let me see if I use async function right here.

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Oh, because if I use the async function, it clearly returns the promise.

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Okay.

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It doesn't have any idea to return another.

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Okay.

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But anyway you canActive right here this will be return a boolean or the promise or the observable boolean.

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Right now we will not focus inside the observable boolean.

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Now, why this here returns a boolean.

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Let me read more about that.

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Now you can see, if it returns a true, the request will be processed.

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If return false, it will deny the request.

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Let me show you how it can be used.

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For example, I can use the @UseGuard inside the controller or we can use something like this.

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Okay, we can mark the class or the instance of class, or we can use global.

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Or something like here, I will discuss this syntax later.

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refactor.

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Okay.

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Anyway let me scroll up a little bit.

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So here, in order to use a "guard" we usually use the decorator will be "@UseGuard" right here.

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If I go to the post controller and I will use the controller @UseGuard

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I will pass the "AuthGuard" my guards

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Insde here, let's see, because this returns true, it will process, right?

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It means this will work.

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But if I return false.

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It doesn't work.

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Right.

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So this is the idea.

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Later I will check if the current user is admin, I will allow it will be delete some

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post or something like this.

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Okay.

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We will authorization using the "Guard" and we can authentication also inside the "Guard" right here the

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okay I think this is the guard.

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So hopefully you understand when we use the guard inside the NestJS application.