How to open external pdf into a Ionic3 frame?

I have to open from an Ionic3 app the PDF files hosted on a remote server.
I want to open these files, if possible, into a frame of the app.
The web server returns the raw PDF files after a call done using the BasicAuthentication:
For example, (with username and password passed in the header)

I’ve tried this:

this.navCtrl.push(BrowserPage, {externalUrl: documentUrl});

where BrowserPage has this code:

<iframe *ngIf="externalUrl" [src]="externalUrl" width="100%" height="100%" frameborder="0" ></iframe>

and it works if Basic Authentication is disabled.

How can I use this method with Basic Authentication?
Does it exist an Angular plugin to show PDF files inside an Ionic app?

Thank you very much