Only check if there are more than or equal to 4 numbers.

modules/identity/src/Volo.Abp.Identity.Domain/Volo/Abp/Identity/IdentityUserManager.cs

@@ -1,6 +1,7 @@
 using System;
 using System.Collections.Generic;
 using System.Linq;
+using System.Numerics;
 using System.Threading;
 using System.Threading.Tasks;
 using JetBrains.Annotations;
@@ -444,12 +445,19 @@ public class IdentityUserManager : UserManager<IdentityUser>, IDomainService
 
         var userName = email.Split('@')[0];
 
-        if (!Options.User.AllowedUserNameCharacters.IsNullOrWhiteSpace() && !userName.All(Options.User.AllowedUserNameCharacters.Contains))
+        if (await ValidateUserNameAsync(userName))
         {
-            // The username contains not allowed characters. So, we are generating a random username.
+            // The username is valid.
+            return userName;
+        }
+
+        if (Options.User.AllowedUserNameCharacters.IsNullOrWhiteSpace())
+        {
+            // The AllowedUserNameCharacters is not set. So, we are generating a random username.
+            tryCount = 0;
             do
             {
-                var randomUserName = await GetRandomUserNameAsync(userName.Length);
+                var randomUserName = userName + RandomHelper.GetRandom(1000, 9999);
                 if ( await ValidateUserNameAsync(randomUserName))
                 {
                     return randomUserName;
@@ -457,18 +465,36 @@ public class IdentityUserManager : UserManager<IdentityUser>, IDomainService
                 tryCount++;
             } while (tryCount < maxTryCount);
         }
-        else if (await ValidateUserNameAsync(userName))
+        else if (!userName.All(Options.User.AllowedUserNameCharacters.Contains))
         {
-            // The username is valid.
+            // The username contains not allowed characters. So, we are generating a random username.
-            return userName;
+            do
+            {
+                var randomUserName = await GetRandomUserNameAsync(userName.Length);
+                if ( await ValidateUserNameAsync(randomUserName))
+                {
+                    return randomUserName;
+                }
+                tryCount++;
+            } while (tryCount < maxTryCount);
         }
-        else if (Options.User.AllowedUserNameCharacters.IsNullOrWhiteSpace() || "0123456789".All(Options.User.AllowedUserNameCharacters.Contains))
+        else if (Options.User.AllowedUserNameCharacters.Where(char.IsDigit).Distinct().Count() >= 4)
         {
-            // The AllowedUserNameCharacters includes numbers. So, we are generating 4 random numbers and appending to the username.
+            // The AllowedUserNameCharacters includes 4 numbers. So, we are generating 4 random numbers and appending to the username.
+            var numbers = Options.User.AllowedUserNameCharacters.Where(char.IsDigit).OrderBy(x => Guid.NewGuid()).Take(4).ToArray();
+            var minArray = numbers.OrderBy(x => x).ToArray();
+            if (minArray[0] == '0')
+            {
+                var secondItem = minArray[1];
+                minArray[0] = secondItem;
+                minArray[1] = '0';
+            }
+            var min = int.Parse(new string(minArray));
+            var max = int.Parse(new string(numbers.OrderByDescending(x => x).ToArray()));
             tryCount = 0;
             do
             {
-                var randomUserName = userName + RandomHelper.GetRandom(1000, 9999);
+                var randomUserName = userName + RandomHelper.GetRandom(min, max);
                 if ( await ValidateUserNameAsync(randomUserName))
                 {
                     return randomUserName;

modules/identity/test/Volo.Abp.Identity.Domain.Tests/Volo/Abp/Identity/IdentityUserManager_Tests.cs

@@ -437,6 +437,12 @@ public class IdentityUserManager_Tests : AbpIdentityDomainTestBase
         username.ShouldContain("admin");
         Regex.IsMatch(username, @"\d{4}$").ShouldBeTrue();
 
+        _identityUserManager.Options.User.AllowedUserNameCharacters = "admin01234";
+        username = await _identityUserManager.GetUserNameFromEmailAsync("admin@abp.io");
+        username.Length.ShouldBe(9); //admin and random 4 numbers
+        username.ShouldContain("admin");
+        Regex.IsMatch(username, @"[0-4]{3}$").ShouldBeTrue();
+
         _identityUserManager.Options.User.AllowedUserNameCharacters = "abcdefghijklmnopqrstuvwxyz";
         username = await _identityUserManager.GetUserNameFromEmailAsync("admin@abp.io");
         username.Length.ShouldBe(9); //admin and random 4 characters