To redirect the traffic from HTTP to HTTPS, the web server configuration should be modified to include a rule that forces the HTTP requests to be redirected to HTTPS. This can be done by using the web server's configuration file or a .htaccess file. The exact syntax may vary depending on the web server software, but the general idea is to use a rewrite rule that matches the HTTP protocol and changes it to HTTPS. For example, on Apache web server, the following code can be added to the .htaccess file:
RewriteEngine On
RewriteCond %{HTTPS} off
RewriteRule ^(.*)$ https://%{HTTP_HOST}%{REQUEST_URI} [L,R=301]
This code will check if the HTTPS is off, and if so, it will rewrite the URL to use HTTPS and redirect the client with a 301 status code, which means permanent redirection. This way, the clients will always use HTTPS to access the web application, and the links generated from the web application will be encrypted.
User account access (A) is not relevant to the redirection of HTTP to HTTPS, as it only controls who can access the web application. Programming code (B) may be used to generate the links with HTTPS, but it will not redirect the existing HTTP requests to HTTPS. Load balancer setting (D) may also be used to redirect the traffic to HTTPS, but it is not the most efficient or secure way, as it will add an extra layer of processing and expose the HTTP traffic to the load balancer. Therefore, web server configuration is the best option to redirect the traffic to HTTPS.