Update a Debian user's password and passkey and grant sudo access

For a user named agaric:

sudo passwd agaric

Enter new UNIX password:
Retype new UNIX password:
passwd: password updated successfully

From a different server with working id_dsa public key that had been cat'd into authorized_keys:

scp authorized_keys ben@example.org:~

Then back on the server to which we're updating this user, from your own home directory to which you just uploaded the authorized keys file.
sudo mv authorized_keys /home/agaric/.ssh

Alternatively (and more likely your situation), get and upload the user's public key, and cat it into authorized_keys, creating that file if necessary. (See creating SSH keys.)

... but, our user still cannot login without a password.

i cannot change the owner of the authorized_keys file. perhaps that's the root of the problem.

To which I responded:

blast! i swear this is documented on Agaric somewhere, i remember this now

ben@example.org:/home/agaric/.ssh$ ls -la

total 20
drwxr-xr-x 2 agaric agaric 4096 Sep 21 16:08 .
drwxr-xr-x 8 agaric agaric 4096 Jul 22 2007 ..
-rw-r--r-- 1 agaric agaric 799 Jul 22 2007 OLD_authorized_keys
-rw-r--r-- 1 ben ben 396 Sep 21 16:02 authorized_keys
-rw-r--r-- 1 agaric agaric 442 Jul 22 2007 known_hosts

ben@example.org:/home/agaric/.ssh$ sudo chown agaric:agaric authorized_keys
ben@example.org:/home/agaric/.ssh$ ls -la

total 20
drwxr-xr-x 2 agaric agaric 4096 Sep 21 16:08 .
drwxr-xr-x 8 agaric agaric 4096 Jul 22 2007 ..
-rw-r--r-- 1 agaric agaric 799 Jul 22 2007 OLD_authorized_keys
-rw-r--r-- 1 agaric agaric 396 Sep 21 16:02 authorized_keys
-rw-r--r-- 1 agaric agaric 442 Jul 22 2007 known_hosts

I let our user know:

ok, it's changed to being owned by you

Test successful!

Now the public key login works.

What else is there to say?

awesome

Now that the user has a secure public key, let's give them sudo privileges.

Adding a user to sudo access, the sudoers file:

Not this way:
sudo vi /etc/sudoers

# This file MUST be edited with the 'visudo' command as root.

This way:

$ su root

Password:

visudo

Resolution