// в App.js в методе render

<Router>
    <Switch>
        <Route exact path='/login' component={Register}/>
        <Route exact path='/auth-complete' component={AuthComplete}/>
        <Route component={DefaultContainer}/>
    </Switch>
</Router>

// Тоже в App.js вне метода
const DefaultContainer = () => (
    <div>
         <SideMenu/>
         <PrivateRoute exact path='/' component={Friends}/>
         <Route component={NotFound}/>
    </div>
 )