[v15] Redirect to root route if logged in

web/packages/teleport/src/Login/Login.story.tsx

@@ -43,6 +43,7 @@ const sample: State = {
     isSuccess: true,
     message: '',
   },
+  checkingValidSession: false,
   onLogin: () => null,
   onLoginWithWebauthn: () => null,
   onLoginWithSso: () => null,

web/packages/teleport/src/Login/Login.tsx

@@ -38,6 +38,7 @@ export function Login({
   onLoginWithSso,
   authProviders,
   auth2faType,
+  checkingValidSession,
   preferredMfaType,
   isLocalAuthEnabled,
   clearAttempt,
@@ -47,6 +48,12 @@ export function Login({
   showMotd,
   acknowledgeMotd,
 }: State) {
+  // while we are checking if a session is valid, we don't return anything
+  // to prevent flickering. The check only happens for a frame or two so
+  // we avoid rendering a loader/indicator since that will flicker as well
+  if (checkingValidSession) {
+    return null;
+  }
   return (
     <>
       <Logo src={logoSrc} />

web/packages/teleport/src/Login/useLogin.ts

@@ -16,16 +16,18 @@
  * along with this program.  If not, see <http://www.gnu.org/licenses/>.
  */
 
-import { useState } from 'react';
+import { useState, useEffect } from 'react';
 import { useAttempt } from 'shared/hooks';
 import { AuthProvider } from 'shared/services';
 
+import session from 'teleport/services/websession';
 import history from 'teleport/services/history';
 import cfg from 'teleport/config';
 import auth, { UserCredentials } from 'teleport/services/auth';
 
 export default function useLogin() {
   const [attempt, attemptActions] = useAttempt({ isProcessing: false });
+  const [checkingValidSession, setCheckingValidSession] = useState(true);
 
   const authProviders = cfg.getAuthProviders();
   const auth2faType = cfg.getAuth2faType();
@@ -44,6 +46,14 @@ export default function useLogin() {
     setShowMotd(false);
   }
 
+  useEffect(() => {
+    if (session.isValid()) {
+      history.replace(cfg.routes.root);
+      return;
+    }
+    setCheckingValidSession(false);
+  }, []);
+
   function onLogin(email, password, token) {
     attemptActions.start();
     auth
@@ -74,6 +84,7 @@ export default function useLogin() {
   return {
     attempt,
     onLogin,
+    checkingValidSession,
     onLoginWithSso,
     authProviders,
     auth2faType,