title: https urls in coherence emails when phoenix is behind a proxy
body: <p>I have my phoenix app set up behind nginx. Nginx is serving https traffic.</p>
  
  <p>I want emails from coherence to contain https urls like <code>https://my_domain.com/...</code>, but I can't figure out how to do so.</p>
  
  <p>Here is my app's config:</p>
  
  <pre><code>config :my_app, MyApp.Endpoint,
    http: [port: 8080],
    url: [host: "my_domain.com", port: 443],
    # ...
  </code></pre>
  
  <p>With this config, urls in emails are like this: <code>my_domain.com:443/some_path</code>. And when I remove <code>port: 443</code>, they became <code>my_domain.com:8080/some_path</code>. And adding <code>force_ssl: [hsts: true]</code> doesn't help too.</p>
  
  <p>Of cource I could set <code>url: [host: "my_domain.com", port: 80]</code> and set nginx to redirect all http requests to port 443, but it seems wrong to me. I could edit email templates to force https urls, but this also seems wrong.</p>
  
  <p>Or maybe using a proxy in front of an erlang app is not an erlang way and I just didn't get it yet?</p>