Install SSL Certificate Microsoft
How to setup Internet Security and Acceleration (ISA) Server to host Web sites using the Secure Sockets Layer (SSL) protocol.
If you are hosting a web site that uses an SSL certificate and you also have an ISA server firewall, you will need to have that same SSL certificate key pair installed on both your IIS web server and the ISA server.
Assuming that you have already installed your SSL certificate on your IIS web server, you can follow the A and B parts of this How To to export your certificate from your IIS server and import it in to your ISA server.
Now that your SSL certificate has been copied over from your IIS web server you will need to configure your ISA server by following the steps outlined in the Microsoft Help & Support Article. Another helpful article can be found at ISAserver.org
Verify Installation
To verify if your certificate is installed correctly, use our Certificate Installation Checker.
Test your SSL certificate by using a browser to connect to your server. Use the https protocol directive. For example, if your SSL was issued to secure.mysite.com, enter https://secure.mysite.com
into your browser.
Your browser's padlock icon will be displayed in the locked position if your certificate is installed correctly and the server is properly configured for SSL.
For IIS SSL troubleshooting, Microsoft has designed a tool - SSL Diagnostics - to aid in quickly identifying configuration problems in the IIS metabase, certificates, or certificate stores.