{% extends '::layout.html.twig' %}

{% block body %}
    <div class="container">
        <div class="row">
            <div class="col-xs-2">
            </div>
            <div class="col-xs-8">
                {% if error %}
                    <div class="alert alert-danger" role="alert">{{ error.messageKey|trans(error.messageData, 'security') }}</div>
                {% endif %}
            </div>
        </div>
        <div class="row">
            <div class="col-xs-4">
            </div>
            <div class="col-xs-4">
                <form action="{{ path('login') }}" method="post">
                    <div class="form-group">
                        <label for="username">Email Address:</label>
                        <input class="form-control" type="text" id="username" name="_username" value="{{ last_username }}" />
                    </div>

                    <div class="form-group">
                        <label for="password">Password:</label>
                        <input class="form-control" type="password" id="password" name="_password" />
                    </div>

                    <input type="hidden" name="_csrf_token" value="{{ csrf_token('authenticate') }}" />
                    {% if redirect is not empty %}
                        <input type="hidden" name="_target_path" value="{{ redirect }}"/>
                    {% endif %}

                    <button class="pull-right btn btn-primary" type="submit">Login</button>
                </form>
            </div>
        </div>
    </div>
{% endblock %}

{% extends '::layout.html.twig' %}

{% block body %}
    <div class="container">
        <div class="row">
            <div class="col-xs-2">
            </div>
            <div class="col-xs-8">
                {% if error %}
                    <div class="alert alert-danger" role="alert">{{ error.messageKey|trans(error.messageData, 'security') }}</div>
                {% endif %}
            </div>
        </div>
        <div class="row">
            <div class="col-xs-4">
            </div>
            <div class="col-xs-4">
                <form action="{{ path('login') }}" method="post">
                    <div class="form-group">
                        <label for="username">Username:</label>
                        <input class="form-control" type="text" id="username" name="_username" value="{{ last_username }}" />
                    </div>

                    <div class="form-group">
                        <label for="password">Password:</label>
                        <input class="form-control" type="password" id="password" name="_password" />
                    </div>

                    <input type="hidden" name="_csrf_token" value="{{ csrf_token('authenticate') }}" />
                    {% if redirect is not empty %}
                        <input type="hidden" name="_target_path" value="{{ redirect }}"/>
                    {% endif %}

                    <button class="pull-right btn btn-primary" type="submit">Login</button>
                </form>
            </div>
        </div>
    </div>
{% endblock %}

Change label on login page 'email' to 'username'
Change label on login page 'email' to 'username'
