Casperjs/Phantomjs Modifying headers

i'm trying to change some headers but nothing is working:

var casper = require('casper').create({ //     stepTimeout: 15000,     verbose: false,     logLevel: 'error',     pageSettings: {         loadImages: true,         loadPlugins: true,         userAgent: 'Mozilla/5.0 (Windows NT 10.0; Win64; x64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/58.0.3029.110 Safari/537.364',        customHeaders: {             Connection: 'keep-alive',             Accept: 'text/html,application/xhtml+xml,application/xml;q=0.9,image/webp,*/*;q=0.8'} } });

I also tried:

phantom.page.customHeaders = { "User-Agent" : "Mozilla/5.0 (X11; Ubuntu; Linux x86_64; rv:26.0) Gecko/20100101 Firefox/26.0", "Accept": "text/html,application/xhtml+xml,application/xml;q=0.9,*/*;q=0.8", "Accept-Language": "en-US,en;q=0.5", "Accept-Encoding": "gzip, deflate","Connection" : "keep-alive" };

And for a single connection:

this.open('http://localhost/post.php', {     method: 'post',     headers: { 'Accept': 'application/json' } });

None of them are working or am i doing something wrong?Thanks