Improve login page

src/pages/AdminLoginPage/AdminLoginPage.tsx

@@ -20,6 +20,7 @@ export interface AdminLoginPageState {
   error: string;
 }
 
+const DEFAULT_REDIRECT = "/admin";
 class AdminLoginPage extends React.Component<AdminLoginPageProps, AdminLoginPageState> {
   constructor(props) {
     super(props);
@@ -90,13 +91,14 @@ class AdminLoginPage extends React.Component<AdminLoginPageProps, AdminLoginPage
     const { search } = location;
     const params = qs.parse(search);
     const { next } = params;
-    return next || "/admin";
+    return next || DEFAULT_REDIRECT;
   }
 
   render() {
     const { username, password, isAuthenticated } = this.state;
+    const next = this.getRedirectURL();
+
     if (isAuthenticated) {
-      const next = this.getRedirectURL();
       return <Redirect to={next} />;
     }
 
@@ -105,6 +107,9 @@ class AdminLoginPage extends React.Component<AdminLoginPageProps, AdminLoginPage
         <Helmet>
           <link rel="canonical" href="https://sik.ayy.fi/admin/login" />
         </Helmet>
+        { next && next !== DEFAULT_REDIRECT && (
+          <div>You have to log in first.</div>
+        ) }
         <form className="admin-login-form" onSubmit={this.handleSubmit}>
           <label>Username
             <input id="login-username" type="text" name="username" value={username} onChange={this.handleUserNameChange} />