sudo git clone git@my.git.server:user/repo.git

sudo -u www-data -H git clone git@my.git.server:user/repo.git

Cloning into 'repo'...
fatal: 'user/repo.git' does not appear to be a git repository
fatal: Could not read from remote repository.

james-c@WebHost-1:~$ sudo ssh -v git@my.git.server 2>&1 | grep 'identity file'
debug1: identity file /root/.ssh/id_rsa type -1
debug1: identity file /root/.ssh/id_rsa-cert type -1
debug1: identity file /root/.ssh/id_dsa type -1
debug1: identity file /root/.ssh/id_dsa-cert type -1
debug1: identity file /root/.ssh/id_ecdsa type -1
debug1: identity file /root/.ssh/id_ecdsa-cert type -1
debug1: identity file /root/.ssh/id_ed25519 type -1
debug1: identity file /root/.ssh/id_ed25519-cert type -1
james-c@WebHost-1:~$ sudo -u www-data ssh -v git@my.git.server 2>&1 | grep 'identity file'
debug1: identity file /var/www/.ssh/id_rsa type 1
debug1: identity file /var/www/.ssh/id_rsa-cert type -1
debug1: identity file /var/www/.ssh/id_dsa type -1
debug1: identity file /var/www/.ssh/id_dsa-cert type -1
debug1: identity file /var/www/.ssh/id_ecdsa type -1
debug1: identity file /var/www/.ssh/id_ecdsa-cert type -1
debug1: identity file /var/www/.ssh/id_ed25519 type -1
debug1: identity file /var/www/.ssh/id_ed25519-cert type -1

sudo -u deploydeputy /bin/bash -c "export HOME=/home/deploydeputy && git clone git@github.com:inventid/cdn.git /tmp/cdn"