title: Need to initialize a constant before gem initialization ( rails 3 and rails 4)
body: <p>I am implementing a omniAuth authentication system through a gem and i would need to initialize a constant before the gem gets loaded. </p>
  
  <p>Scenario:</p>
  
  <p>The developer should write that constant in a config file, restart its server and that constant should be initialized before the gem gets loaded.</p>
  
  <p>I tried to put it in a <code>config/initializers/omniauth.rb</code> file but i get a error when loading the server </p>
  
  <pre><code>unitialized constant OmniAuth::Strategies::Xyz::URL.
  </code></pre>
  
  <p>i am writting it in the gem in this manner:</p>
  
  <pre><code>OmniAuth::Strategies::Xyz::URL= "http://my_account.com"
  </code></pre>