Michals answer worked for me, albeit with one small modification:

Problem:

when you have a single site security certificate, a browser that tries to access your page without https:// www. (or whichever domain your certificate covers) will display an ugly red warning screen before it even gets to receive the redirect to the safe and correct https page.

Solution

First use the redirect to the www (or whichever domain is covered by your certificate) and only then do the https redirect. This will ensure that your users are not confronted with any error because your browser sees a certificate that doesn't cover the current url.

#First rewrite any request to the wrong domain to use the correct one (here www.)

RewriteCond %{HTTP_HOST} !^www.

RewriteRule ^(.*)$ https://www.%{HTTP_HOST}%{REQUEST_URI} [L,R=301]



#Now, rewrite to HTTPS:

RewriteCond %{HTTPS} off

RewriteRule ^(.*)$ https://%{HTTP_HOST}%{REQUEST_URI} [L,R=301]

If you are using CloudFlare or a similar CDN you will get an infinite loop error with the %{HTTPS} solutions provided here. If you're a CloudFlare user you'll need to use this:

RewriteEngine On

RewriteCond %{HTTP:X-Forwarded-Proto} =http

RewriteRule ^ https://%{HTTP_HOST}%{REQUEST_URI} [L,R=301]

BAD SOLUTION AND WHY!

Don't ever use the solution above because when you are using their code that is something like:

RewriteCond %{HTTPS} off

RewriteRule .* https://%{HTTP_HOST}%{REQUEST_URI} [L,R=301]



RewriteCond %{HTTP_HOST} !^www. [NC]

RewriteRule .* https://www.example.com%{REQUEST_URI} [L,R=301]

The browser goes to:

http://example.com

Then redirects to:

https://example.com

Then redirects to:

https://www.example.com

This is too much request to the server

BEST SOLUTION AND THE ANSWER

This code has an [OR] condition to prevent dual changes at url!

RewriteEngine on

RewriteCond %{HTTPS} off [OR]

RewriteCond %{HTTP_HOST} !^www. [NC]

RewriteRule (.*) https://www.example.com%{REQUEST_URI} [R=301,L]

Most of the answers even accepted one, don't use this trick.

This is the best way I found for Proxy and not proxy users

RewriteEngine On



### START WWW & HTTPS



# ensure www.

RewriteCond %{HTTP_HOST} !^www. [NC]

RewriteRule ^ https://www.%{HTTP_HOST}%{REQUEST_URI} [L,R=301]



# ensure https

RewriteCond %{HTTP:X-Forwarded-Proto} !https

RewriteCond %{HTTPS} off

RewriteRule ^ https://%{HTTP_HOST}%{REQUEST_URI} [L,R=301]



### END WWW & HTTPS

There are a lot of solutions out there. Here is a link to the apache wiki which deals with this issue directly.

http://wiki.apache.org/httpd/RewriteHTTPToHTTPS

RewriteEngine On

# This will enable the Rewrite capabilities



RewriteCond %{HTTPS} !=on

# This checks to make sure the connection is not already HTTPS



RewriteRule ^/?(.*) https://%{SERVER_NAME}/$1 [R,L]

# This rule will redirect users from their original location, to the same location but using HTTPS.

# i.e.  http://www.example.com/foo/ to https://www.example.com/foo/

# The leading slash is made optional so that this will work either in httpd.conf

# or .htaccess context

To redirect http:// or https:// to https://www you can use the following rule on all versions of apache :

RewriteEngine on



RewriteCond %{HTTPS} off [OR]

RewriteCond %{HTTP_HOST} !^www.

RewriteRule ^ https://www.example.com%{REQUEST_URI} [NE,L,R]

Apache 2.4

RewriteEngine on



RewriteCond %{REQUEST_SCHEME} http [OR]

RewriteCond %{HTTP_HOST} !^www.

RewriteRule ^ https://www.example.com%{REQUEST_URI} [NE,L,R]

Note that The %{REQUEST_SCHEME} variable is available for use since apache 2.4 .

If you are on CloudFlare, make sure you use something like this.

# BEGIN SSL Redirect

<IfModule mod_rewrite.c>

RewriteEngine On

RewriteCond %{HTTP:X-Forwarded-Proto} =http

RewriteRule ^ https://%{HTTP_HOST}%{REQUEST_URI} [L,R=301]

</IfModule>

# END SSL Redirect

This will save you from the redirect loop and will redirect your site to SSL safely.

P.S. It is a good idea to if check the mod_rewrite.c!

Set in your .htaccess file

RewriteEngine On

RewriteCond %{HTTP_HOST} !^www.

RewriteRule ^(.*)$ https://www.%{HTTP_HOST}/$1 [R=301,L]

RewriteCond %{HTTPS} !=on

RewriteRule ^ https://%{HTTP_HOST}%{REQUEST_URI} [L,R=301]

I try first answer and it doesnt work...
This work:

<IfModule mod_rewrite.c>

RewriteEngine On

RewriteBase /



RewriteCond %{ENV:HTTPS} !=on

RewriteRule ^.*$ https://%{SERVER_NAME}%{REQUEST_URI} [R,L]



# BEGIN WordPress

<IfModule mod_rewrite.c>

RewriteEngine On

RewriteBase /

RewriteRule ^index.php$ - [L]

RewriteCond %{REQUEST_FILENAME} !-f

RewriteCond %{REQUEST_FILENAME} !-d

RewriteRule . /index.php [L]

</IfModule>



# END WordPress

RewriteEngine On

RewriteCond %{HTTP_HOST} !^www.

RewriteRule ^(.*)$ https://www.%{HTTP_HOST}/$1 [R=301,L]

Notes: Make sure you have done the following steps

1. sudo a2enmod rewrite


2. sudo service apache2 restart


3. Add Following in your vhost file, located at /etc/apache2/sites-available/000-default.conf

<Directory /var/www/html>

  Options Indexes FollowSymLinks MultiViews

  AllowOverride All

  Order allow,deny

  allow from all

  Require all granted

</Directory>

Now your .htaccess will
work and your site will redirect to http:// to https://www

RewriteEngine On 

RewriteCond %{SERVER_PORT} 80 

RewriteRule ^(.*)$ https://%{HTTP_HOST}%{REQUEST_URI} [L,R]

This will work for both https and www

RewriteCond %{HTTPS} !=on

# This checks to make sure the connection is not already HTTPS

RewriteRule ^/?(.*) https://%{HTTP_HOST}%{REQUEST_URI} [R,L]