HTTPS access to RT-N66U (merlin's fw)

[pirx73]

If i use HTTPS to access my router's management web page from LAN, i get warning that certificate is invalid, chain broken. In short - default certificate in firmware is incorrect. Also, HTTPS access works very slowly, i suspect due to broken certificate chain.
How can i fix that?
I understand i can install correct certificate but i have no idea how to generate correct certificate, i suppose i also need a CA?
I found good instructions how to install certificate in router but they all presume one already has certificates.
Could someone please explain how to generate CA and certificate and sign them i guess?

 

[smadremanden]

this is a bit outdated but should work
https://www.rickygao.com.au/blog/get-a-free-public-ssl-for-your-lab/