Fix logout link to be dynamically generated

.env.example

 REACT_APP_API_URL=http://stackspin_proxy:8081/api/v1
-REACT_APP_HYDRA_PUBLIC_URL=https://sso.init.stackspin.net

src/components/Header/Header.tsx

-import React, { Fragment, useState } from 'react';
+import React, { Fragment, useMemo, useState } from 'react';
 import { Disclosure, Menu, Transition } from '@headlessui/react';
 import { MenuIcon, XIcon } from '@heroicons/react/outline';
 import { useAuth } from 'src/services/auth';
@@ -26,8 +26,6 @@ function filterNavigationByDashboardRole(isAdmin: boolean) {
   return navigation.filter((item) => !item.requiresAdmin);
 }
 
-const HYDRA_URL = process.env.REACT_APP_HYDRA_PUBLIC_URL;
-
 // eslint-disable-next-line @typescript-eslint/no-empty-interface
 interface HeaderProps {}
 
@@ -50,7 +48,15 @@ const Header: React.FC<HeaderProps> = () => {
 
   const navigationItems = filterNavigationByDashboardRole(isAdmin);
 
-  const signOutUrl = `${HYDRA_URL}/oauth2/sessions/logout`;
+  // eslint-disable-next-line react-hooks/exhaustive-deps
+  const signOutUrl = useMemo(() => {
+    const { hostname } = window.location;
+    // If we are developing locally, we need to use the init cluster's public URL
+    if (hostname === 'localhost') {
+      return `https://sso.init.stackspin.net/oauth2/sessions/logout`;
+    }
+    return `https://sso.${hostname.replace('dashboard', '')}/oauth2/sessions/logout`;
+  }, []);
 
   return (
     <>