@Injectable({
    providedIn: 'root'
})
export class AuthService {
 private user: string = null;

    getUser() {
        return this.user;
    }

    setUser(username) {
        sessionStorage.setItem('username',username);
        this.user = sessionStorage.getItem('username');
        console.log('VAMOS!!!', this.user);
    }

async ngOnInit() {
        console.log('HOY', this.authService.getUser());
    }

VAMOS!!! string
HOY null