How to force drupal 7 to load HTTPS assets?
Solutions
if everything(SERVER AND HOST SETTINGS) is ok just $conf['https'] = TRUE; in your settings.php.
According to Enabling HTTP Secure (HTTPS)
Drupal configuration :
If you want to support mixed-mode HTTPS and HTTP sessions open up sites/default/settings.php and add $conf['https'] = TRUE;. This enables you use the same session over HTTP and HTTPS both -- but with two cookies where the HTTPS cookie is sent over HTTPS only. You will need to use contributed modules like securepages to do anything useful with this mode, like submitting forms over HTTPS and so on. While your HTTP cookie is still vulnerable to all usual attacks, a hijacked insecure session cookie can only be used to gain authenticated access to the HTTP site. It will not be valid on the HTTPS site. Whether this is a problem or not depends on the needs of your site and the various module configurations. For example, if all forms are set to go through HTTPS and your visitors can see the same information as logged in users then this is not a problem.
For even better security, leave $conf['https'] at the default value (FALSE) and send all authenticated traffic through HTTPS and use HTTP for anonymous sessions. Once again contributed modules like Secure Login or 443 Session can help you here. Drupal 7 automatically enables the session.cookie_secure PHP configuration on HTTPS sites, which causes SSL-only secure session cookies to be issued to the browser. For best-possible security, set up your site to only use HTTPS, and respond to all HTTP requests with a redirect to your HTTPS site. $conf['https'] can be left at its default value (FALSE) on pure-HTTPS sites. Even then, HTTPS is vulnerable to man-in-the-middle attacks if the connection starts out as a HTTP connection before being redirected to HTTPS. Use the HSTS module or set the Strict-Transport-Security header in your webserver to help prevent users from accessing the site without HTTPS.
also you can use Secure Pages module
Description of module :
A small process which will redirect the required pages to a SSL version of the page.
Update
also you can in settings.php do: $base_url = 'https://'.$_SERVER['SERVER_NAME'];.
I updated settings.php with: $base_url = 'https://'.$_SERVER['SERVER_NAME'];
The Secure Pages module does this.
A small process which will redirect the required pages to a SSL version of the page.