In Angular, an interceptor is a middleware that intercepts HTTP requests and responses. Interceptors are used to manipulate or transform HTTP requests and responses globally. This means you can modify HTTP requests and responses in one place and affect all the requests and responses that go through that place.

Ininterceptors In Angular
Interceptors are a powerful tool in Angular as they can be used for a wide variety of tasks, such as,
    Adding authorization headers to requests
    Logging requests and responses
    Adding or removing parameters from requests
    Transforming response data

How to implement an interceptor in Angular?
To implement an interceptor in Angular, you need to create a class that implements the HttpInterceptor interface. The HttpInterceptor interface has two methods to implement: intercept() and, optionally, handleError().

So let's start. Here's an example of an interceptor that adds an authorization header to every HTTP request,
import { Injectable } from '@angular/core';
import { HttpInterceptor, HttpRequest, HttpHandler, HttpEvent } from '@angular/common/http';
import { Observable } from 'rxjs';

@Injectable()
export class AuthInterceptor implements HttpInterceptor {
    intercept(request: HttpRequest < any > , next: HttpHandler): Observable < HttpEvent < any >> {
        // Get the access token from your authentication service
        const accessToken = this.authService.getAccessToken();
        // Clone the request and add the authorization header
        const authRequest = request.clone({
            headers: request.headers.set('Authorization', `Bearer ${accessToken}`)
        });
        // Pass the cloned request to the next handler in the chain
        return next.handle(authRequest);
    }
}

In this example, the AuthInterceptor class implements the HttpInterceptor interface and overrides the intercept() method. In the intercept() method, we get the access token from our authentication service and clone the incoming request, adding an authorization header. We then pass the cloned request to the next handler in the chain using the next.handle() method.

To use this interceptor, register it with the Angular HTTP client. You can do this by providing it in the provider's array of your AppModule,
import { NgModule } from '@angular/core';
import { BrowserModule } from '@angular/platform-browser';
import { HttpClientModule, HTTP_INTERCEPTORS } from '@angular/common/http';

import { AuthInterceptor } from './auth.interceptor';

@NgModule({
    imports: [BrowserModule, HttpClientModule],
    providers: [{
        provide: HTTP_INTERCEPTORS,
        useClass: AuthInterceptor,
        multi: true
    }]
})
export class AppModule {}

In this example, we import the HttpClientModule and our AuthInterceptor class. We then provide our interceptor in the provider's array using the HTTP_INTERCEPTORS token. The multi-option is set to true, which means that this interceptor is added to the existing array of HTTP interceptors rather than replacing it.
Benefits of using interceptors in Angular

    Interceptors allow the manipulation of HTTP requests and responses globally, making it easy to implement cross-cutting concerns such as authentication and error handling.
    Interceptors can reduce code duplication by providing a centralized place to modify requests and responses.
    Interceptors can be easily added or removed, making it easy to change the behavior of your application without having to modify every HTTP request and response.

Summary
Interceptors are a powerful Angular tool that allows you to manipulate HTTP requests and responses globally. They can be used for various tasks and provide a centralized place to modify requests and responses. By using interceptors, you can reduce code duplication and easily add or remove functionality from your application.