title: Codeigniter CSRF sometimes throwing error
body: <p>First of all, this <strong>rarely happens</strong>. The form itself was submitted successfully 500+ times. And we received about 3 reports where users get a <em>"An Error was encountered: The action you have requested is not allowed"</em>.</p>
  
  <p>This specific error can be found in the Security Class php code, and is only shown when <strong>the csrf tokens do not mach, or if one or both (cookie/post) are missing</strong>.</p>
  
  <p>Here are some relevant config values:</p>
  
  <pre><code>$config['cookie_prefix'] = 'prefix_';
  $config['cookie_domain'] = '';
  $config['cookie_path'] = '/';
  $config['cookie_secure'] = FALSE;
  $config['cookie_httponly'] = FALSE;
  $config['csrf_protection'] = TRUE;
  $config['csrf_token_name'] = 'csrf';
  $config['csrf_cookie_name'] = 'csrf';
  $config['csrf_expire'] = 86400;
  $config['csrf_regenerate'] = FALSE;
  </code></pre>
  
  <p>As said, in almost all cases, users have no issue submitting the form. When a user does have an issue, I tried to replicate the error by submitting the form myself, using <strong>identical input values</strong> and <strong>identical browser/os</strong> (cookies and javascript enabled, without browser plugins). But I wasn't able to simulate the error.</p>
  
  <p>What could be causing Codeigniter to sometimes throw an error?</p>