implemented returning to page the client was at before starting oidc login

frontend/src/Components/Login.svelte

@@ -39,7 +39,7 @@
     async function redirectTo(e,service){
         const btn = e.target;
         btn.disabled = true;
-        const url  = api(`user/oidc/redirect/${service}`);
+        const url  = api(`user/oidc/redirect/${service}?returnTo=${window.location.pathname}`);
         const resp = await fetch(url,{credentials:'include'});
         if (resp.ok){
             const json = await resp.json();