Implementation of a web service for exchanging data with an external site with incomplete SSL / TLS support?

Question

PHP

A question in a more technical context to the experts, from whom I would like to receive an answer and their opinion. Programming language based on PHP and JS.

What technology to choose today to enable communication between two sites , given that the protocol is not completely over SSL?

Explanation of the project:
My clients can be different sites where the module developed by me will be displayed, respectively sending me requests and receiving in response the data to be displayed.

Clients: www.SAIT1.ru, www.SAIT2.ru, www.SAIT3.ru, etc... (HTTP protocol) My program: MYAPP
(HTTPS protocol)

).
All these sites are usually on HTTP protocol, and for example, if a user on a client site wants to log in, or simply log in in the login form, he will have to fill in the login data that is transmitted to my MYAPP site that is on HTTPS protocol.
Once MYAPP sees the request, it will respond with user-friendly information.

Question 1: Which technology or method to choose?

Question 2: How to implement the two protocols HTTP and HTTPS?

On my site, it will be possible to log in with identical MYAPP data that was entered in the login block inserted on the client sites.

**** UPDATED **** Same

functionality as Facebook Login or Twitter Login .

The user, being on SITE1 , can add a certain product to his cart, the information is transmitted to my module located on their website.

Here, respectively, the question is, What is the appropriate way to choose to place the BASKET module:

• via IFRAME
  
• via SCRIPT , as in the example of Google Analytics, place tags on the site so that the script sends data to my module/site/composition every time it is clicked
  

An additional challenge is, if possible, to minimize the actions that clients will have to take on their sites hosting my module.

**** UPDATED 2****

After analyzing different technologies, I chose the most suitable one in my opinion: Node.js and Socket.io .
Correct me if I'm wrong.

There are key questions to be addressed in order to make a final decision on node.js :

• Is it possible to connect MOISITE to an external site SITE1 or SITE2... ?
  
• Is it possible to transfer data through a socket from one site to another site?
  
• How to secure connection between external nodes/sockets?
  
• Is it possible to transfer Session / Cache / Cookies from one node to another external one?
  

I will test and unsubscribe, I will be very grateful for your comments and advice.

Answer 1

Question 2: How to implement the two protocols HTTP and HTTPS?

You don't need to implement anything, the upgrade from http to https is automatic and transparent. Problems would be with downgrade.

Question 1: Which technology or method to choose?

The standard answer is what you know.
If instead of chaotic implementation details you described the essence of the task, you could probably advise something else.

Answer 2

if I understand you correctly, then you can read here and here , everything is written down in sufficient detail, on the second link even with examples from ready-made widgets.