Allow email to be retrieve by SSO ReverseProxy

If REMOTE_EMAIL header is set, use it as user email.
If REVERSE_PROXY_DEFAULT_DOMAIN is set but not REMOTE_EMAIL, use the current construct.

app/Core/Http/Request.php

@@ -270,6 +270,17 @@ class Request extends Base
         return $this->getServerVariable(REVERSE_PROXY_USER_HEADER);
     }
 
+    /**
+     * Get remote email
+     *
+     * @access public
+     * @return string
+     */
+    public function getRemoteEmail()
+    {
+        return $this->getServerVariable(REVERSE_PROXY_EMAIL_HEADER);
+    }
+
     /**
      * Returns query string
      *