How to access private channel

[Lo Peter]

Dear all,

I am experimenting with setting up a private channel as a private
github repository, then I prepared a channels file for testing:

(list (channel
       (name 'guix)
       (url "https://git.savannah.gnu.org/git/guix.git";)
       (commit "9904a15a4c838362673c1affdbaf1e83d92fe8ff"))
      (channel
       (name 'my-guix-pkgs)
       (url "g...@github.com:peterloleungyau/my-guix-pkgs.git")
       (commit "b51d236ebbbdd134bafb64e5092342a2d058ec2a")))

Then I try it with:
$ guix time-machine -C channels.scm --disable-authentication --
environment --ad-hoc python-radian
Updating channel 'guix' from Git repository at
'https://git.savannah.gnu.org/git/guix.git'...
guix time-machine: warning: channel authentication disabled
Updating channel 'my-guix-pkgs' from Git repository at
'g...@github.com:peterloleungyau/my-guix-pkgs.git'...
guix time-machine: error: Git error: Failed to retrieve list of SSH
authentication methods: Failed getting response


So it seems the guix daemon cannot use the SSH of my user to access
the private git repository? How to get around this? Thanks in advance.

Regards,
Peter Lo