form.html

    用来显示登录表单的模板：

    <html>

    <head>

    <title>Please Sign In</title>

    </head>

    <body>

    {% if message %}

    <p style="color:red">{{ message }}</p>

    {% endif %}

    <form action="/signin" method="post">

    <legend>Please sign in:</legend>

    <p><input name="username" placeholder="Username" value="{{ username }}"></p>

    <p><input name="password" placeholder="Password" type="password"></p>

    <p><button type="submit">Sign In</button></p>

    </form>

    </body>

    </html>