Angular Content-Security-Policy Header and JavaScript

When building a web application in Angular, it's important to consider security measures to protect your users' data and your application from attacks. One of the security measures that you can implement is a Content Security Policy (CSP).

A CSP is a set of rules that a website follows to prevent cross-site scripting attacks (XSS), clickjacking attacks, and other code injection attacks. It tells the browser which resources are allowed to be loaded and executed, and determines which scripts can execute on a particular page.

How to Set Content-Security-Policy Header in Angular

In Angular, you can set the CSP header by using the APP_INITIALIZER provider to set the header before the application is bootstrapped.

Here's an example of how to implement CSP in Angular:

1. Create a new file called csp.ts in your app directory.
2. Add the following code:

import { Injectable } from '@angular/core';
import { DOCUMENT } from '@angular/common';

@Injectable({
  providedIn: 'root'
})
export class CspService {
  constructor(@Inject(DOCUMENT) private readonly document: Document) {}

  public setCSP() {
    const csp = 'default-src \'self\'; img-src *';
    this.document.defaultView?.addEventListener('load', () => {
      this.document.defaultView?.addEventListener('load', () => {
        const meta = this.document.createElement('meta');
        meta.setAttribute('http-equiv', 'Content-Security-Policy');
        meta.setAttribute('content', csp);
        this.document.head.appendChild(meta);
      });
    });
  }
}

This code generates a CSP meta tag and appends it to the head of the document. You can replace the default-src and img-src with your desired policy.

3. In your app.module.ts file, add the following:

import { APP_INITIALIZER } from '@angular/core';
import { CspService } from './csp.service';

export function setCspHeader(cspService: CspService) {
  return () => cspService.setCSP();
}

@NgModule({
  declarations: [
    AppComponent
  ],
  imports: [
    BrowserModule
  ],
  providers: [
    // Set CSP header before the application is bootstrapped
    {
      provide: APP_INITIALIZER,
      useFactory: setCspHeader,
      deps: [CspService],
      multi: true
    },
    CspService
  ],
  bootstrap: [AppComponent]
})
export class AppModule { }

After adding these changes, the CSP header will be automatically set when the application is loaded.

Conclusion

In conclusion, using a CSP header in your Angular application can add an extra layer of security and prevent common attacks like XSS and clickjacking. By implementing CSP, you can control which scripts can be executed and protect your users' data.