added simple validation

lib/screens/auth/login_page.dart

@@ -11,10 +11,12 @@ class AuthorizationPage extends StatefulWidget {
 class _AuthorizationPage extends State<AuthorizationPage> {
   final TextEditingController _loginController = new TextEditingController();
   final TextEditingController _passwordController = new TextEditingController();
+  final _formKey = GlobalKey<FormState>();
   final borederRadius = BorderRadius.all(Radius.circular(10));
   bool passwordVisible = false;
 
   void _login(){
+    if (_formKey.currentState!.validate()) {
       final String login = _loginController.text;
       final String password  = _passwordController.text;
 
@@ -24,6 +26,23 @@ class _AuthorizationPage extends State<AuthorizationPage> {
         );
       }
     }
+  }
+
+  String? _validatePassword(String? password){
+    if (password == null || password.isEmpty)
+      return 'Введите пароль';
+    if (password != '123456')
+      return 'Пароль: 123456';
+    return null;
+  }
+
+    String? _validateLogin(String? login){
+    if (login == null || login.isEmpty)
+      return 'Введите логин';
+    if (login != 'admin')
+      return 'Логин: admin';
+    return null;
+  }
 
   @override
   void dispose() {
@@ -61,20 +80,22 @@ class _AuthorizationPage extends State<AuthorizationPage> {
   }
 
   Widget _buildFormWidget(BuildContext context) {
-    return Column(
+    return Form(
+      key: _formKey,
+      child: Column(
         children: [
-          TextField(
+          TextFormField(
             controller: _loginController,
             decoration: InputDecoration(
               prefixIcon: Icon(Icons.account_circle),
               border: OutlineInputBorder(
                 borderRadius: borederRadius
               ), 
-              labelText: 'Логин'
+              labelText: 'Логин'),
-              )
+              validator: (text) => _validateLogin(text),
           ),
           SizedBox(height: 25,),
-          TextField(
+          TextFormField(
             controller: _passwordController,
             obscureText: !passwordVisible,
             decoration: InputDecoration(
@@ -85,17 +106,13 @@ class _AuthorizationPage extends State<AuthorizationPage> {
               labelText: 'Пароль',
               suffixIcon: IconButton(
                 icon: Icon(
-                  passwordVisible ? Icons.visibility : Icons.visibility_off
+                  passwordVisible ? Icons.visibility : Icons.visibility_off),
-                  ),
+              onPressed: () => setState(() => passwordVisible = !passwordVisible),
-              onPressed: () {
+            )),
-                setState(() {
+            validator: (text) => _validatePassword(text),
-                  passwordVisible = !passwordVisible;
-                });
-              }
-            )
-            )
         ),
         ],
+      )
     );
   }
 }