What causes a "CLIENT_UNAUTHORIZED [769]" login error?

1. To fix it, add following 2 lines to /etc/ssh/sshd_config

TrustedUserCAKeys /etc/ssh/lightsail_instance_ca.pub  
  
CASignatureAlgorithms +ssh-rsa  

2. Restart

/etc/init.d/ssh restart  

Problem
Log in failed. If this instance has just started up, try again in a minute or two.

CLIENT_UNAUTHORIZED [769]

I too was facing this issue and found the exact steps to fix it (comparing a lightsail instanced that was working)
This is without opening the other settings

Step 1) Download the default key
Step 2) Connect using a terminal app with that key
Step 3) sudo nano /etc/ssh/sshd_config
Step 4) Add Include /etc/ssh/sshd_config.d/*.conf
I put it around line 10 - there is a gap there between a bunch of commented items
Step 5) At the very bottom you should see TrustedUserCAKeys /etc/ssh/lightsail_instance_ca.pub
Add CASignatureAlgorithms +ssh-rsa on the next line
Step 6) Ctrl + X to save and exit
Step 7) sudo service ssh restart

The web terminal should now work

Hello,

I have lost my default key and my browser-based SSH also not working. What can I do in this case?

One possible reason for this error is the system clock on your instance being out of sync with reality. If that's the case, https://forums.aws.amazon.com/thread.jspa?messageID=812946 is a similar issue.

If you can login into your instance using PuTTY, please try checking the system clock. If it drifted too much, Lightsail in-browser SSH will not be able to connect.

If this keeps happening, please consider setting up https://en.wikipedia.org/wiki/Ntpd on your instances.

Over a year later, I know. I am having the same error, on a brand new Lightsail instance. The timezone, date, and time are set to mine, which is the same as the instance region. I am also running chrony to keep time in synchronisation.

Same Problem here. Any ideas?
Thanks a lot!

I had the same issue after I upgraded Ubuntu from 18.04 to 20.04.

I believe this is due to recent changes on ssh that stopped supporting RSA/SHA1 CA algorithm.
Although there is a risk, you can allow it explicitly for now. Maybe it's better to upload another public key.

https://sarunas-krisciukaitis.medium.com/hashicorp-vault-ssh-secret-engine-with-openssh-8-2-and-later-f7405ee55d19

This solved it for me. Thanks for the info.

This solved it for me too, after an upgrade from Ubuntu 18 to Ubuntu 20. Thanks!

Edited by: RigaDorje on Apr 7, 2021 11:26 AM

Thanks,
helpful