[@ionic/core] How to implement route guard?

How is the recommended way to implement secure routes (one route that is secure has, initially, a redirect to a login page that is erased from the navigation stack as soon as the user is logged in).

Check here for the angular docs on CanActivate:
Angular CanActivate

For Ionic v4, you will want to add
canActivate: [AuthGuard]
to the specific route you want to protect

then you want to create an auth.guard.ts file that interacts with your authentication service/provider and implements the ‘canActivate’ method to return a boolean value whether the user can navigate to the intended route:

import { Injectable } from '@angular/core';
import { Router, CanActivate } from '@angular/router';
import { AuthService } from './auth.service';

@Injectable() // guards are services
export class AuthGuardService implements CanActivate {   // needs to implement CanActivate

  constructor(public auth: AuthService, public router: Router) {}

  canActivate(): boolean {    
    if (!this.auth.isAuthenticated()) {    // method in auth service to determine user status
      this.router.navigate(['login']);     // redirects to login page
      return false;                        // desired page 'cannot activate'

    return true; // desired page 'can activate' if user is logged

Thank you, but I’m using @ionic/core (with StencilJS), not Angular.

Ah sorry about the misunderstanding

Is this what you’re looking for?
StencilJS - Router redirect