{{ form_start(loginForm) }}

<div class="form-group ">
    <div class="input-group">
        <div class="input-group-addon"><i class="fa fa-envelope"></i></div>
        {{ form_row(loginForm._username,{
            "attr":{
                "class":"col-md-4"
            }
        }) }}
    </div>
</div>
<div class="form-group ">
    <div class="input-group">
        <div class="input-group-addon"><i class="fa fa-lock"></i></div>
        {{ form_row(loginForm._password,{
            "label":false,
            "attr":{
                "class":"col-md-4",
                "placeholder":"Password"
            }
        }) }}
    </div>
</div>

<input type="submit" value="Login" class="btn btn-success btn-custom">

{{ form_end(loginForm) }}