How to install custom SSL certificates on an ASUS RT-N66U running asuswrt-merlin

gistfile1.txt

###########################################
# IMPORTANT NOTE:
#
# As of asuswrt-merlin 380.67 Beta, you
# can now configure SSL certificates from
# the Webui, making these instructions
# unnecessary.
###########################################



# First, enable SSH in the Administration->System tab.
# Then log in to the device.

# Verify that https_crt_save is off
admin@RT-N66U:/tmp/home/root# nvram get https_crt_save
0

# Enable https_crt_save and verify that it was set correctly
admin@RT-N66U:/tmp/home/root# nvram set https_crt_save=1
admin@RT-N66U:/tmp/home/root# nvram get https_crt_save
1

# Write your custom key and certificate to the ephemeral file system.
# Note that these files will not be preserved on restart.
admin@RT-N66U:/tmp/home/root# cat >/etc/key.pem
# paste in key
admin@RT-N66U:/tmp/home/root# cat >/etc/cert.pem
# paste in cert

# Verify https_crt_file is empty
admin@RT-N66U:/tmp/home/root# nvram get https_crt_file
admin@RT-N66U:/tmp/home/root#

# Restart httpd. When httpd starts up with https_crt_save enabled, it does the
# following: If /etc/cert.pem and /etc/key.pem exist, it tars them together and
# saves them in https_crt_file.  If they do not exist (this would be the case
# on reboot) and https_crt_file exists, httpd will extract the contents of
# https_crt_file. You can see how this works in the start_ssl function here:
# https://github.com/RMerl/asuswrt-merlin/blob/master/release/src/router/httpd/httpd.c
admin@RT-N66U:/tmp/home/root# service restart_httpd

# Ensure https_crt_file is now full
admin@RT-N66U:/tmp/home/root# nvram get https_crt_file
# ...snip...

# Reboot AP to make sure cert is put back on boot
admin@RT-N66U:/tmp/home/root# reboot

From this thread it seems EC certificates are not accepted so only RSA. I've used RSA2048. Also, make sure you don't concatene intermediate certificate, the certificate uploaded should be the one given by acme, nothing more nothing less.

This! This turned out to be the problem for me, on stock firmware at least. When I generated my certificates with "--key-type rsa" with certbot, the below commands worked without any problems. I used the exact same commands before on Asusmerlin, and that worked with EC certificates. But I had to revert back to stock firmware, and tried to import my own certificates again, but it did not work. So I think that Merlin has implemented them, but Asus hasn't (yet). Could that be the case?
I am on the ZenWifi XT-8, but I imagine this also goes for the RT-N66U.

So in short:
Copy cert files to:
/jffs/.cert/cert.pem
/jffs/.cert/key.pem
Restart the service
service restart_httpd

Its been a while since I have been in the gist, but for anyone using a Lets Encrypt certificate this script below combined with the following acme.sh command gets a working internal certificate
acme.sh --home /jffs/acme.sh --issue -d example.com --dns dns_cf --debug --fullchain-file /etc/cert.pem --key-file /etc/key.pem --reloadcmd "/jffs/acme.sh/installcertificate.sh"

/jffs/acme.sh/installcertificate.sh

#!/bin/sh
tar -C / -czf /jffs/cert.tgz etc/cert.pem etc/key.pem
nvram set https_crt_save=1
service restart_httpd