Changing body background color based on authentication

I am building an Ember application. On my homepage page my body background color is our website's blue, but when a user logs in, I want the body background color to change to white. How can I set a dynamic body background color that changes after a user is authenticated?

Here is my body css:

body {
    background-color: $process-blue;
    font-family: 'Lato', sans-serif;
    @include container(80%);
}