User limit enforcement (#26511)

* Added hard limits when creating user

* Added check to user activation

* Added missing check for licensed servers

* Fix i18n

* Fixed style order

* Added a separate hard limit along with existing 10k user soft limit

* For CI

* Fixing flaky test, hopefully

* Added tests

server/channels/app/user_test.go

@@ -2008,3 +2008,160 @@ func TestGetUsersForReporting(t *testing.T) {
 		require.NotNil(t, userReports)
 	})
 }
+
+func TestCreateUserOrGuest(t *testing.T) {
+	t.Run("base case - you can create a user", func(t *testing.T) {
+		th := Setup(t)
+		defer th.TearDown()
+
+		user := &model.User{
+			Email:         "TestCreateUserOrGuest@example.com",
+			Username:      "username_123",
+			Nickname:      "nn_username_123",
+			Password:      "Password1",
+			EmailVerified: true,
+		}
+		createdUser, appErr := th.App.createUserOrGuest(th.Context, user, false)
+		require.Nil(t, appErr)
+		require.Equal(t, "username_123", createdUser.Username)
+	})
+
+	t.Run("cannot create user when user count has exceeded the permissible limit", func(t *testing.T) {
+		th := SetupWithStoreMock(t)
+		defer th.TearDown()
+
+		mockUserStore := storemocks.UserStore{}
+		mockUserStore.On("Count", mock.Anything).Return(int64(12000), nil)
+
+		mockStore := th.App.Srv().Store().(*storemocks.Store)
+		mockStore.On("User").Return(&mockUserStore)
+
+		user := &model.User{
+			Email:         "TestCreateUserOrGuest@example.com",
+			Username:      "username_123",
+			Nickname:      "nn_username_123",
+			Password:      "Password1",
+			EmailVerified: true,
+		}
+		createdUser, appErr := th.App.createUserOrGuest(th.Context, user, false)
+		require.NotNil(t, appErr)
+		require.Nil(t, createdUser)
+	})
+
+	t.Run("can create user when server is exactly on limit", func(t *testing.T) {
+		th := SetupWithStoreMock(t)
+		defer th.TearDown()
+
+		id := NewTestId()
+		userCreationMocks(t, th, id, 11000)
+
+		user := &model.User{
+			Email:         "TestCreateUserOrGuest@example.com",
+			Username:      "username_123",
+			Nickname:      "nn_username_123",
+			Password:      "Password1",
+			EmailVerified: true,
+		}
+		createdUser, appErr := th.App.createUserOrGuest(th.Context, user, false)
+		require.Nil(t, appErr)
+		require.Equal(t, "username_123", createdUser.Username)
+	})
+
+	t.Run("licensed server can create user when server is OVER limit", func(t *testing.T) {
+		th := SetupWithStoreMock(t)
+		defer th.TearDown()
+
+		id := NewTestId()
+		userCreationMocks(t, th, id, 20000)
+
+		user := &model.User{
+			Email:         "TestCreateUserOrGuest@example.com",
+			Username:      "username_123",
+			Nickname:      "nn_username_123",
+			Password:      "Password1",
+			EmailVerified: true,
+		}
+
+		th.App.Srv().SetLicense(model.NewTestLicense(""))
+		createdUser, appErr := th.App.createUserOrGuest(th.Context, user, false)
+		require.Nil(t, appErr)
+		require.Equal(t, "username_123", createdUser.Username)
+	})
+
+	t.Run("licensed server can create user when server is UNDER limit", func(t *testing.T) {
+		th := SetupWithStoreMock(t)
+		defer th.TearDown()
+
+		id := NewTestId()
+		userCreationMocks(t, th, id, 10)
+
+		user := &model.User{
+			Email:         "TestCreateUserOrGuest@example.com",
+			Username:      "username_123",
+			Nickname:      "nn_username_123",
+			Password:      "Password1",
+			EmailVerified: true,
+		}
+
+		th.App.Srv().SetLicense(model.NewTestLicense(""))
+		createdUser, appErr := th.App.createUserOrGuest(th.Context, user, false)
+		require.Nil(t, appErr)
+		require.Equal(t, "username_123", createdUser.Username)
+	})
+}
+
+func userCreationMocks(t *testing.T, th *TestHelper, userID string, activeUserCount int64) {
+	mockUserStore := storemocks.UserStore{}
+	mockUserStore.On("Count", mock.Anything).Return(activeUserCount, nil)
+	mockUserStore.On("IsEmpty", mock.Anything).Return(false, nil)
+	mockUserStore.On("VerifyEmail", mock.Anything, "TestCreateUserOrGuest@example.com").Return("", nil)
+	mockUserStore.On("InvalidateProfilesInChannelCacheByUser", mock.Anything).Return()
+	mockUserStore.On("InvalidateProfileCacheForUser", mock.Anything).Return()
+	mockUserStore.On("Save", mock.Anything, mock.Anything).Return(&model.User{
+		Id:            userID,
+		Email:         "TestCreateUserOrGuest@example.com",
+		Username:      "username_123",
+		Nickname:      "nn_username_123",
+		Password:      "Password1",
+		EmailVerified: true,
+	}, nil)
+
+	mockUserStore.On("Get", mock.Anything, userID).Return(&model.User{
+		Id:            userID,
+		Email:         "TestCreateUserOrGuest@example.com",
+		Username:      "username_123",
+		Nickname:      "nn_username_123",
+		Password:      "Password1",
+		EmailVerified: true,
+	}, nil)
+
+	mockGroupStore := storemocks.GroupStore{}
+	mockGroupStore.On("GetByName", "username_123", mock.Anything).Return(nil, nil)
+
+	mockChannelStore := storemocks.ChannelStore{}
+	mockChannelStore.On("InvalidateAllChannelMembersForUser", mock.Anything).Return()
+
+	mockPreferencesStore := storemocks.PreferenceStore{}
+	mockPreferencesStore.On("Save", mock.Anything).Return(nil)
+
+	mockProductNoticeStore := storemocks.ProductNoticesStore{}
+	mockProductNoticeStore.On("View", userID, mock.Anything).Return(nil)
+
+	mockStore := th.App.Srv().Store().(*storemocks.Store)
+	mockStore.On("User").Return(&mockUserStore)
+	mockStore.On("Group").Return(&mockGroupStore)
+	mockStore.On("Channel").Return(&mockChannelStore)
+	mockStore.On("Preference").Return(&mockPreferencesStore)
+	mockStore.On("ProductNotices").Return(&mockProductNoticeStore)
+
+	var err error
+	th.App.ch.srv.userService, err = users.New(users.ServiceConfig{
+		UserStore:    &mockUserStore,
+		SessionStore: &storemocks.SessionStore{},
+		OAuthStore:   &storemocks.OAuthStore{},
+		ConfigFn:     th.App.ch.srv.platform.Config,
+		LicenseFn:    th.App.ch.srv.License,
+	})
+
+	require.NoError(t, err)
+}