Send a variable to HTML with express sendfile (short question)

I'm using Node.JS, path, and express to run an HTML webpage and need to send a variable to the HTML for its use:

var client_cred_access_token = 'fakeToken';

...

app.get('/', function (req, res) {
    res.sendFile(path.join(__dirname, '/public', 'homepage.html'));
});

How can I send this string variable to homepage.html?