Module development and code questions

I'm currently trying to integrate my website into another set of non-PHP back-end code.  I want to use the drupal authentication process, and then trigger certain external activities based on the logged in user.

I had this working under D7 as follows:

1. Get the cookie name - namely, 

strCookieName = "SESS" & Left(sha256(strCookieDomain),32)

2. Read the cookie value

3. Go to the MySQL database, and get the username that cookie belongs to:

Good evening, I'm using drupal 8 and I would like to add the classic Welcome to user in the user menu. in drupal 7 I added a block with php and voila but drupal8 I understand that it does not. My question is is there a module that does it or if there is any way to do it.

slds

My Story:

I'm from Symfony. I have an old symfony4 site. It's an Online Examination Website. I'm maintaining it for years. Now I planned to migrate to Drupal8.

Drupal is amazing and I have developed and hosted two simple sites. It's really great.

Noted: I'm new to Drupal8 and I'm learning it.

Current work: (My work related to this question)

I have a requirement to build several forms of which many require 2 or even 3-column (with a search button inline after a textfield). I'm amazed at how difficult such a trivial task has become - I've been scratching my head for days with unbelievable layouts staring me in the face - none really looking like a modern web form should look...

Hi. I cannot get separate label and value from Commerce product

I wish get label and value from product.variation_sku like this:

<div>
<div>{{ product.variation_sku.label }} </div>
<div>{{ product.variation_sku.value }} </div>
</div>

but it not work. I tried change product.variation_sku.label with product.variation_sku.title but nothing. Please how can get this value?

Error Message:

warning: mail(): SMTP server response: 503 Bad sequence of commands. You must specify the recipients of a message before you can send it. includes\common.inc on line 2127.

HAS BEEN FIXED PLEASE DISREGARD. Thank you