Force SSL/https using .htaccess and mod_rewrite

For Apache, you can use mod_ssl to force SSL with the SSLRequireSSL Directive:

This directive forbids access unless HTTP over SSL (i.e. HTTPS) is enabled for the current connection. This is very handy inside the SSL-enabled virtual host or directories for defending against configuration errors that expose stuff that should be protected. When this directive is present all requests are denied which are not using SSL.

This will not do a redirect to https though. To redirect, try the following with mod_rewrite in your .htaccess file

RewriteEngine On
RewriteCond %{HTTPS} !=on
RewriteRule ^ https://%{HTTP_HOST}%{REQUEST_URI} [L,R=301]

or any of the various approaches given at

• http://www.askapache.com/htaccess/http-https-rewriterule-redirect.html

You can also solve this from within PHP in case your provider has disabled .htaccess (which is unlikely since you asked for it, but anyway)

if (!isset($_SERVER['HTTPS']) || $_SERVER['HTTPS'] !== 'on') {
    if(!headers_sent()) {
        header("Status: 301 Moved Permanently");
        header(sprintf(
            'Location: https://%s%s',
            $_SERVER['HTTP_HOST'],
            $_SERVER['REQUEST_URI']
        ));
        exit();
    }
}

PHP Solution

Borrowing directly from Gordon's very comprehensive answer, I note that your question mentions being page-specific in forcing HTTPS/SSL connections.

function forceHTTPS(){
  $httpsURL = 'https://'.$_SERVER['HTTP_HOST'].$_SERVER['REQUEST_URI'];
  if( count( $_POST )>0 )
    die( 'Page should be accessed with HTTPS, but a POST Submission has been sent here. Adjust the form to point to '.$httpsURL );
  if( !isset( $_SERVER['HTTPS'] ) || $_SERVER['HTTPS']!=='on' ){
    if( !headers_sent() ){
      header( "Status: 301 Moved Permanently" );
      header( "Location: $httpsURL" );
      exit();
    }else{
      die( '<script type="javascript">document.location.href="'.$httpsURL.'";</script>' );
    }
  }
}

Then, as close to the top of these pages which you want to force to connect via PHP, you can require() a centralised file containing this (and any other) custom functions, and then simply run the forceHTTPS() function.

HTACCESS / mod_rewrite Solution

I have not implemented this kind of solution personally (I have tended to use the PHP solution, like the one above, for it's simplicity), but the following may be, at least, a good start.

RewriteEngine on

# Check for POST Submission
RewriteCond %{REQUEST_METHOD} !^POST$

# Forcing HTTPS
RewriteCond %{HTTPS} !=on [OR]
RewriteCond %{SERVER_PORT} 80
# Pages to Apply
RewriteCond %{REQUEST_URI} ^something_secure [OR]
RewriteCond %{REQUEST_URI} ^something_else_secure
RewriteRule .* https://%{SERVER_NAME}%{REQUEST_URI} [R=301,L]

# Forcing HTTP
RewriteCond %{HTTPS} =on [OR]
RewriteCond %{SERVER_PORT} 443
# Pages to Apply
RewriteCond %{REQUEST_URI} ^something_public [OR]
RewriteCond %{REQUEST_URI} ^something_else_public
RewriteRule .* http://%{SERVER_NAME}%{REQUEST_URI} [R=301,L]

I found a mod_rewrite solution that works well for both proxied and unproxied servers.

If you are using CloudFlare, AWS Elastic Load Balancing, Heroku, OpenShift or any other Cloud/PaaS solution and you are experiencing redirect loops with normal HTTPS redirects, try the following snippet instead.

RewriteEngine On

# If we receive a forwarded http request from a proxy...
RewriteCond %{HTTP:X-Forwarded-Proto} =http [OR]

# ...or just a plain old http request directly from the client
RewriteCond %{HTTP:X-Forwarded-Proto} =""
RewriteCond %{HTTPS} !=on

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

Mod-rewrite based solution :

Using the following code in htaccess automatically forwards all http requests to https.

RewriteEngine on

RewriteCond %{HTTPS}::%{HTTP_HOST} ^off::(?:www\.)?(.+)$
RewriteRule ^ https://www.%1%{REQUEST_URI} [NE,L,R]

This will redirect your non-www and www http requests to www version of https.

Another solution (Apache 2.4*)

RewriteEngine on

RewriteCond %{REQUEST_SCHEME}::%{HTTP_HOST} ^http::(?:www\.)?(.+)$
RewriteRule ^ https://www.%1%{REQUEST_URI} [NE,L,R]

This doesn't work on lower versions of apache as %{REQUEST_SCHEME} variable was added to mod-rewrite since 2.4.