Open the Internet Services Manager and right-click on Default Web Site (or the site hosting your OWA component.) Select Properties.

Under the Directory Security tab, click Server Certificate.

Click Next. Select Create A New Certificate and hit Next. 

Select Prepare The Request Now, But Send It Later and hit Next.

Enter a name for the certificate that you can identify on your server. Choose a bit-length of 2048. Leave the other boxed unchecked.

Enter the full legal name of your company. Enter a department such as Security or IT in the organizational unit.

Enter the fully qualified domain name of your Outlook Web Access (ex. mail.yourdomain.com).  Note: If you are generating this for a wildcard certificate, use *.yourdomain.com

Enter the location of your organization: Country, State, and City.

Choose a file name and a location to save your Certificate Signing Requst (CSR). The file should be saved as a text file (.txt)

Click Next to generate the file.

Now open the CSR file using a text editor such as notepad and copy/paste the text (including the BEGIN and END tags) into the order form.