Centering FontAwesome icons vertically and horizontally

I'm currently using FontAwesome, and am having a really hard time centering the icons both vertically and horizontally in their container. I have tried doing it via positioning and ran into issues bc the icon sizes were different. I basically have the horizontal, and am trying to get the vertical.

<div class='container'>
    <div class='row'>
        <div class='offset2 span6 loginContainer'>
            <div class='row'>
                <div class='login-icon'>    
                    <i class='icon-user'></i>
                </div>
                <input type="text"  placeholder="Email" />

            </div>
            <div class='row'>
                <div class='login-icon'><i class=" icon-lock "></i></div>
                <input type="password" class="" placeholder="Password" />
            </div>
        </div>
    </div>
</div>

.login-icon{
    font-size: 40px;
    line-height: 40px;
    background-color:black;
    color:white;
    width: 50px;
    height: 50px;

}
.login-icon [class*='icon-']{
  height: 50px;
  width: 50px;
  display: inline-block;
  text-align: center;
  vertical-align: baseline;
}

http://jsfiddle.net/ncapito/e2UPC/

This is all you need, no wrapper needed:

.login-icon{
    display:inline-block;
    font-size: 40px;
    line-height: 50px;
    background-color:black;
    color:white;
    width: 50px;
    height: 50px;
    text-align: center;
    vertical-align: bottom;
}

http://jsfiddle.net/e2UPC/6/

I have used transform to correct the offset. It works great with round icons like the life ring.

<span class="fa fa-life-ring"></span>

.fa {
    transform: translateY(-4%);
}

the simplest solution to both horizontally and vertically centers the icon:

<div class="d-flex align-items-center justify-content-center">
    <i class="fas fa-crosshairs fa-lg"></i>
</div>