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How do one configure a splash disclaimer page on a Cisco Wireless Controller 5508 with no authentication?
There are many options to you in this scenario, but if you're looking to simply provide a splash page via the WLC without interacting with any other web servers, you can configure Local Web Authentication (LWA) as seen in this configuration example.
If you are not wanting the authentication, you can choose the "passthrough" method which will not require any credentials, only accepting an AUP or whatever you want.