Added the ability to log out

Requested by Evelyn and Melissa of MIIS.

go.php

@@ -25,6 +25,7 @@
 	"gotionary.php",
 	"gobacktionary.php",
 	"login.php",
+	"logout.php",
 	"go_functions.php",
 	"process.php",
 	"all_codes.php",

header_midd.php

@@ -93,8 +93,8 @@
                 print "<a href='login.php?r=".urlencode(curPageURL())."'>Log in</a>";
               }
             } else {
-              //print "<a href='https://login.middlebury.edu/cas/logout'>Log Out</a>";
               print "<a href='admin.php'>Manage GO</a>";
+              print " | <a href='logout.php'>Log Out</a>";
             }
           ?>
         </section>

header_miis.php

@@ -209,8 +209,8 @@
                 print "<a href='login.php?r=".urlencode(curPageURL())."'>Log in</a>";
               }
             } else {
-              //print "<a href='https://login.middlebury.edu/cas/logout'>Log Out</a>";
               print "<a href='admin.php'>Manage GO</a>";
+              print " | <a href='logout.php'>Log Out</a>";
             }
           ?>
         </nav>

logout.php

@@ -0,0 +1,28 @@
+<?php
+
+require_once "config.php";
+require_once "go.php";
+
+// Unset all of the session variables.
+$_SESSION = array();
+// If it's desired to kill the session, also delete the session cookie.
+// Note: This will destroy the session, and not just the session data!
+if (ini_get("session.use_cookies")) {
+    $params = session_get_cookie_params();
+    setcookie(session_name(), '', time() - 42000,
+        $params["path"], $params["domain"],
+        $params["secure"], $params["httponly"]
+    );
+}
+session_destroy();
+
+$dest = $institutions[$institution]['base_uri'];
+
+if (AUTH_METHOD == 'cas') {
+	GoAuthCas::configurePhpCas();
+	phpCAS::logoutWithRedirectServiceAndUrl($dest, $dest);
+}
+
+//redirect on completion
+header("location: ".$dest);
+exit;