How do I insert user id in an associative table?

I have three table, campaign, places and campaign_place, the primary keys in campaign and place are used inside campaign_place as foriegn keys plus the campaign_place table has it's own id column and the user_id column.

I have setup the proper many to many relationships using BelongsToMany in campaign and place models.

1- I define a number of places, and then I go and create a campaign. I have a multi select box which is populated by the places created by the logged in user.

2- What I am trying to achieve is that when I save the campaign the places selected in the multiselect are also saved in the associative table with user_id.

currently I am successfully saving all the data in campaigns, places and in the associative table of campaign_place as well.

The only thing I am confused about is saving the user_id in the associative table as well because at this time its not being saved.

Following is the code:

Create form for campaigns:

{!! Form::open(array('route' => 'campaigns.store')) !!}

                        {{Form::label('campaignName','Campaign Name:' )}}
                        {{Form::text('campaignName', null, array('class' => 'form-control', 'placeholder'=>'Name of your campaign')) }}

                        {{Form::label('campaignDescription','Campaign Description:' )}}
                        {{Form::textarea('campaignDescription', null, array('class' => 'form-control', 'rows' => '2', 'placeholder'=>'Provide a small description of your campaign...')) }}

                        <div class="col-lg-6">

                            {{Form::label('startDate','Start Date:' )}}
                            {{Form::date('startDate', null, array('class' => 'form-control')) }}

                        </div>

                        <div class="col-lg-6">
                            {{Form::label('endDate','End Date:' )}}
                            {{Form::date('endDate', null, array('class' => 'form-control')) }}
                        </div>

                        {{Form::label('title','Campaign Title:' )}}
                        {{Form::text('title', null, array('class' => 'form-control', 'id' => 'title','placeholder'=>'This will appear in your mobile')) }}

                        {{Form::label('places','Assign Places:' )}}
                        <select class="form-control select2-multi" name="places[]" multiple="multiple">
                            @foreach (auth()->user()->places as $place)
                                <option value='{{ $place->id }}'>{{ $place->name }}</option>
                            @endforeach
                        </select>

                        {{Form::label('notificationText','Notification Text:' )}}
                        {{Form::text('notificationText', null, array('class' => 'form-control')) }}

                        {{Form::label('body','Campaign Body:' )}}
                        {{Form::textarea('body', null, array('class' => 'form-control', 'rows' => '3')) }}

                        {{Form::hidden('user_id', Auth::user()->id)}}


                        {{Form::submit('Save Campaign', array('class' => 'btn btn-success btn-lg btn-block', 'style' => 'margin-top: 20px;'))}}

                        {!! Form::close() !!}

Code for the models:

<?php

namespace App;

use Illuminate\Database\Eloquent\Model;

class Campaign extends Model
{
    protected $fillable=['user_id','campaignName','campaignDescription','startDate','endDate','title','notificationText','body'];

    public function places()
    {
        return $this->belongsToMany('App\Place');
    }
}

Place model:

<?php

namespace App;

use Illuminate\Database\Eloquent\Model;

class Place extends Model
{
    protected $fillable=['name','description','ownedssid','ownedmacaddress', 'ownedrssival', 'lat', 'lng','gfenceradius','country','city','citycode'];

    public function campaigns()
    {
        return $this->belongsToMany('App\Campaign');
    }


}

Code for store function in campaign controller:

    public function store(Request $request)
    {
        // dd($request);

        $this->validate($request, array(
            'campaignName' =>'required|max:255',
            'startDate'    =>'required',
            'endDate'      =>'required',
            'title'      =>'required',
            'notificationText'      =>'required',
            'body'          =>'required'

        ));
        $user = Auth::user();
        $campaign = new Campaign;

        $campaign->campaignName = $request->campaignName;
        $campaign->campaignDescription = $request->campaignDescription;
        $campaign->startDate = $request->startDate;
        $campaign->endDate = $request->endDate;
        $campaign->title = $request->title;
        $campaign->notificationText = $request->notificationText;
        $campaign->body = $request->body;
        $campaign->user_id = $request->user_id;


        $campaign->save();
        $campaign->places()->sync($request->places, false);

    }

Can you please help!

thanks in advance