Cisco 8821 Manual page 151

Once the phone has registered to CUCM, set Web Admin to Enabled in CUCM to enable the admin webpage interface.
Then configure Admin Password by specifying a 8-127 character string.
If wanting to keep the admin webpage interface access enabled long-term, then should utilize a secure profile with TFTP
encryption enabled.
For out of box (factory reset), will need to ensure the date and time is configured correctly.
Can set the Date & Time by syncing to the local machine or setting the Date & Time manually.
Can utilize either the internal Manufacturing Installed Certificate (MIC) or a custom User Installed certificate to be used as the
User Certificate for EAP-TLS.
Cisco Wireless IP Phone 8821 and 8821-EX Wireless LAN Deployment Guide
151