Module development and code questions

Hello, I'm currently working on creating custom error pages on Drupal 9.

I know I can easily add customized pages for 404 and 403, but how can I use custom pages for all possible errors like 401, 403, 500, 502, and etc.?

I found this module: https://www.drupal.org/project/error_page but I couldn't see the result, not so sure which part I messed up with. And some say I could add custom hooks - but I'm not familiar with php and twig, so it was very hard for me to follow with no detailed guidance.

Hi,

I am looking for which SAML module to use for my need : automatically connect to a Drupal 9 site users connected from a client authentication platform (custom client system) with their profile information.
The customer connects from his unique portal and can then choose which application to use, he will be connected with his information.
Is SAML the best choice and which module would you recommend ?

Thanks

Hello. 

I have this code in hook form alter:

Hello,

I am developing a module with a block where I create a selection using the Client-side Hierarchical Select module.
It works so far, the selected values are specified in the path as intended and I can access them in the controller.

Hello,

I am using webforms in which I have created a custom form and a custom module where I make various modifications. My client asked whether is possible while some users to be able to test the form (they belong to a specific role) while the form is closed. What I tried so far is these two things:

• In my custom module hook_form_alter I insert the following code: 

function customvisit_form_alter(&$form, FormStateInterface $form_state, $form_id) {

Hi, i need the key of selected autocomplete when arrive to my controller, but whenever submit the form only send the value and not the key

Is it possible to send the key from the webform? I am using the webform's default post handler

Incomming Currently data :

Array
(
    [create_new_group] => 0
    [select_group] => Group one
    [group_name] => 
    [create_default_subgroup] => 
    [subgroup_name] => sdasdasdas
)

Incomming expected data :