If you host WordPress site on Azure Web App on Linux running Apache, here are the steps to implement HTTP to HTTPS redirect:

1. Add RewriteRule in .htaccess in WordPress application root

 RewriteCond %{HTTP:X-ARR-SSL} ^$
 RewriteRule ^(.*)$ https://%{HTTP_HOST}%{REQUEST_URI} [L,R=301]

2. Once this RewriteRule is added, you may see wp-admin page lost style like this, this is caused by loading mixed content from http and https,

Here is a way to fix this, add following code in wp-config.php,

define('FORCE_SSL_ADMIN', true); 
if ( isset($_SERVER['HTTP_X_ARR_SSL']) ) 
        $_SERVER['HTTPS']='on';