The cPanel keeps prompting the login dialog over and over, and I’m 100% sure the username and password is correct.

Tested with :

  1. WHM 62.0 (build 8)
  2. cPanel 62.0.9

Solution – Cookie IP Validation

To fix it, login WHM, under “Server Configuration” –>> Tweak Settings –>> Security tab –>> Cookie IP Validation, update to “disabled” or “loose“.

Done.

Cloudflare
The root cause is the server hostname is routed through Cloudflare, and causing the IP address is keep on changing during the routing process, and if cPanel IP validation is enabled, you will never able to login successfully.

To fix it, change the “A” record for server hostname at Cloudflare to point directly at your server IP x.x.x.x, rather than having it be a CNAME pointing to the domain name. Otherwise, just disable the cPanel IP validation like above.

References

  1. cPanel – Tweak Settings – Security