Implement password policy for account creation

lib/models/server_config.dart

@@ -4,6 +4,35 @@ import 'package:flutter/widgets.dart';
 ///
 /// @author Pierre Hubert
 
+class PasswordPolicy {
+  final bool allowMailInPassword;
+  final bool allowNameInPassword;
+  final int minPasswordLength;
+  final int minNumberUpperCaseLetters;
+  final int minNumberLowerCaseLetters;
+  final int minNumberDigits;
+  final int minNumberSpecialCharacters;
+  final int minCategoriesPresence;
+
+  const PasswordPolicy({
+    @required this.allowMailInPassword,
+    @required this.allowNameInPassword,
+    @required this.minPasswordLength,
+    @required this.minNumberUpperCaseLetters,
+    @required this.minNumberLowerCaseLetters,
+    @required this.minNumberDigits,
+    @required this.minNumberSpecialCharacters,
+    @required this.minCategoriesPresence,
+  })  : assert(allowMailInPassword != null),
+        assert(allowNameInPassword != null),
+        assert(minPasswordLength != null),
+        assert(minNumberUpperCaseLetters != null),
+        assert(minNumberLowerCaseLetters != null),
+        assert(minNumberDigits != null),
+        assert(minNumberSpecialCharacters != null),
+        assert(minCategoriesPresence != null);
+}
+
 class ServerDataConservationPolicy {
   final int minInactiveAccountLifetime;
   final int minNotificationLifetime;
@@ -28,9 +57,12 @@ class ServerDataConservationPolicy {
 }
 
 class ServerConfig {
+  final PasswordPolicy passwordPolicy;
   final ServerDataConservationPolicy dataConservationPolicy;
 
   const ServerConfig({
+    @required this.passwordPolicy,
     @required this.dataConservationPolicy,
-  }) : assert(dataConservationPolicy != null);
+  })  : assert(passwordPolicy != null),
+        assert(dataConservationPolicy != null);
 }