Update channel permissions for v4 endpoints (#5829)

* Fix join channel permission for v4 endpoint

* Allow regular users to get public channels they are not in

* Fix unit test

api4/apitestlib.go

@@ -25,14 +25,15 @@ import (
 )
 
 type TestHelper struct {
-	Client        *model.Client4
-	BasicUser     *model.User
-	BasicUser2    *model.User
-	TeamAdminUser *model.User
-	BasicTeam     *model.Team
-	BasicChannel  *model.Channel
-	BasicChannel2 *model.Channel
-	BasicPost     *model.Post
+	Client              *model.Client4
+	BasicUser           *model.User
+	BasicUser2          *model.User
+	TeamAdminUser       *model.User
+	BasicTeam           *model.Team
+	BasicChannel        *model.Channel
+	BasicPrivateChannel *model.Channel
+	BasicChannel2       *model.Channel
+	BasicPost           *model.Post
 
 	SystemAdminClient *model.Client4
 	SystemAdminUser   *model.User
@@ -135,6 +136,7 @@ func (me *TestHelper) InitBasic() *TestHelper {
 	me.LoginTeamAdmin()
 	me.BasicTeam = me.CreateTeam()
 	me.BasicChannel = me.CreatePublicChannel()
+	me.BasicPrivateChannel = me.CreatePrivateChannel()
 	me.BasicChannel2 = me.CreatePublicChannel()
 	me.BasicPost = me.CreatePost()
 	me.BasicUser = me.CreateUser()
@@ -145,6 +147,8 @@ func (me *TestHelper) InitBasic() *TestHelper {
 	app.AddUserToChannel(me.BasicUser2, me.BasicChannel)
 	app.AddUserToChannel(me.BasicUser, me.BasicChannel2)
 	app.AddUserToChannel(me.BasicUser2, me.BasicChannel2)
+	app.AddUserToChannel(me.BasicUser, me.BasicPrivateChannel)
+	app.AddUserToChannel(me.BasicUser2, me.BasicPrivateChannel)
 	app.UpdateUserRoles(me.BasicUser.Id, model.ROLE_SYSTEM_USER.Id)
 	me.LoginBasic()