SSH agent will not start on login

Question

I've got an issue where ssh-agent does not start automatically on login. I have tried writing a service, configuring a systemd autostart script and a bunch of other things.

Another thing I've noticed, is that even if I run eval $(ssh-agent -s), the agent will only work until I restart the terminal. Closing and opening the terminal again, then running ssh-add -l gives the dreaded Could not open a connection to your authentication agent. message.

The service that I wrote, with some guidance, looks like this:

[Unit]
Description=SSH agent (ssh-agent)

[Service]
Type=simple
Environment="SSH_AUTH_SOCK=%t/ssh-agent.socket"
Environment="DISPLAY=:0"
ExecStart=ssh-agent -D -a $SSH_AUTH_SOCK
ExecStop=kill -15 $MAINPID

[Install]
WantedBy=default.target

However, it doesn't work, despite starting and running successfully. Here's the systemctl output:

>> systemctl --user status ssh-agent
● ssh-agent.service - SSH agent (ssh-agent)
     Loaded: loaded (/home/david/.config/systemd/user/ssh-agent.service; enabled; preset: enabled)
     Active: active (running) since Mon 2023-01-30 20:08:14 GMT; 9min ago
    Process: 10959 ExecStartPost=/bin/sleep 3 (code=exited, status=0/SUCCESS)
   Main PID: 10958 (ssh-agent)
      Tasks: 1 (limit: 18864)
     Memory: 840.0K
        CPU: 8ms
     CGroup: /user.slice/user-1000.slice/[email protected]/app.slice/ssh-agent.service
             └─10958 ssh-agent -D -a /run/user/1000/ssh-agent.socket

Jan 30 20:08:11 pleb-box systemd[839]: Starting SSH agent (ssh-agent)...
Jan 30 20:08:11 pleb-box ssh-agent[10958]: SSH_AUTH_SOCK=/run/user/1000/ssh-agent.socket; export SSH_AUTH_SOCK;
Jan 30 20:08:11 pleb-box ssh-agent[10958]: echo Agent pid 10958;
Jan 30 20:08:14 pleb-box systemd[839]: Started SSH agent (ssh-agent).

>> echo $SSH_AGENT_PID


>> echo $SSH_AUTH_SOCK


>> ssh-add -l
Could not open a connection to your authentication agent.

As you can see, it doesn't even export the two environment variables, despite it being the second log line. Trying to echo them, returns empty values. I use zsh, but this happens on bash too.

Here's some of my system information:

>> uname -a
Linux pleb-box 5.15.89-1-MANJARO #1 SMP PREEMPT Wed Jan 18 20:37:11 UTC 2023 x86_64 GNU/Linux

>> zsh --version
zsh 5.9 (x86_64-pc-linux-gnu)

>> konsole --version
konsole 22.12.1

>> systemctl --version
systemd 252 (252.4-2-manjaro)
+PAM +AUDIT -SELINUX -APPARMOR -IMA +SMACK +SECCOMP +GCRYPT +GNUTLS +OPENSSL +ACL +BLKID +CURL +ELFUTILS +FIDO2 +IDN2 -IDN +IPTC +KMOD +LIBCRYPTSETUP +LIBFDISK +PCRE2 -PWQUALITY +P11KIT -QRENCODE +TPM2 +BZIP2 +LZ4 +XZ +ZLIB +ZSTD +BPF_FRAMEWORK +XKBCOMMON +UTMP -SYSVINIT default-hierarchy=unified

>> ssh -v localhost
OpenSSH_9.1p1, OpenSSL 3.0.7 1 Nov 2022
...

Any help would be greatly appreciated.