O CUPS não exige o certificado SSL. Você pode desativar os https adicionando DefaultEncryption Never
ao arquivo de configuração e reiniciando o daemon. Nas versões recentes do CentOS (você não especificou a versão que está executando), há uma caixa de seleção "Permitir administração remota" na interface da Web que fornecerá acesso remoto à página de administração do CUPS na porta 631. No seu caso, navegue até: link
Aqui está o arquivo padrão do CUPS que tenho a tendência de implantar em novos sistemas.
MaxLogSize 2000000000
LogLevel info
SystemGroup sys root
# Allow remote access
Port 631
Listen /var/run/cups/cups.sock
# Disable printer sharing and shared printers.
Browsing Off
DefaultAuthType Basic
<Location />
Allow ALL
Allow all
# Allow remote administration...
Order allow,deny
Allow all
</Location>
<Location /admin>
Allow ALL
Allow all
# Allow remote administration...
Order allow,deny
Allow all
</Location>
<Location /admin/conf>
AuthType Default
Require user @SYSTEM
Allow ALL
Allow all
# Allow remote access to the configuration files...
Order allow,deny
Allow all
</Location>
<Policy default>
<Limit Send-Document Send-URI Hold-Job Release-Job Restart-Job Purge-Jobs Set-Job-Attributes Create-Job-Subscription Renew-Subscription Cancel-Subscription Get-Notifications Reprocess-Job Cancel-Current-Job Suspend-Current-Job Resume-Job CUPS-Move-Job>
Require user @OWNER @SYSTEM
Order deny,allow
</Limit>
<Limit CUPS-Add-Modify-Printer CUPS-Delete-Printer CUPS-Add-Modify-Class CUPS-Delete-Class CUPS-Set-Default>
AuthType Default
Require user @SYSTEM
Order deny,allow
</Limit>
<Limit Pause-Printer Resume-Printer Enable-Printer Disable-Printer Pause-Printer-After-Current-Job Hold-New-Jobs Release-Held-New-Jobs Deactivate-Printer Activate-Printer Restart-Printer Shutdown-Printer Startup-Printer Promote-Job Schedule-Job-After CUPS-Accept-Jobs CUPS-Reject-Jobs>
AuthType Default
Require user @SYSTEM
Order deny,allow
</Limit>
<Limit CUPS-Authenticate-Job>
Require user @OWNER @SYSTEM
Order deny,allow
</Limit>
<Limit All>
Order deny,allow
</Limit>
</Policy>
DefaultEncryption Never