This assumes you use WCS to manage your WLC’s. If you don’t then it’s still possible to add a custom WebAuth page to your WLC but we wont be covering that today!
First off build your custom authentication page! You can download a bundle of example’s from Cisco here, you’ll need these as they have the authentication script embedded.
Here’s one I made earlier:
If you’d prefer you can download my custom page here it’s had most of the junk removed compared to the Cisco one.
Once you have your custom page (with or without cats) you need to compress it along with any images into a tar file called WebAuth.tar.
Next login to your WCS and navigate to Configure -> Controller Template Launch Pad -> Security -> Web Auth Configuration
Click on the template name or create a new one.
Under general settings name your template and choose “Customized Web Auth” as the Web Auth Type.
Select “Apply to Controllers” and select the WLC’s you wish to apply this template/custom page to.
Once you have selected controllers you will be prompted to download the new WebAuth.tar bundle to the WCS. You can do this directly from your local machine using the “browse” button or you can upload your .tar file to a TFTP server and copy it across from there.
Your done, if you like you can now preview the new page by logging into a WLC going to Security->WebAuth and selecting preview.