pam-nss-signedjit reads a signed (via CMS) file from an HTTPS endpoint and applies the file to local NSS and PAM files for the purposes of enabling Just-in-Time (JIT) administration.

It intended to be used with:

• ssh keys via AuthorizedKeysCommand
• PAM listfile for authorization / JIT
• NSS extrausers for user and group (admin / sudoers group) info
• pam_mkhomedir for homedir creation

First make a bootstrap.json and also a signed json file uploaded to the url in bootstrap.json. This can be done either via:

• openssl

gzip bootstrap.example.json
openssl cms -sign -in cat bootstrap.example.json.gz -text -outform pem -out jit.signed -signer acert.pem

• via certsign.ps1

It can be validated with either powershell/.NET CMS or via openssl:

openssl cms -verify -in jit.signed -inform pem -out bootstrap.example.json.gz -certfile acert.pem -noverify -nointern
gunzip bootstrap.example.json.gz

Next on client machines:

1. cp pam-nss-signedjit /usr/local/bin/pam-nss-signedjit
2. mkdir /var/lib/pam-nss-signedjit && mkdir /etc/pam-nss-signedjit
3. /usr/local/bin/pam-nss-signedjit bootstrap --filepath bootstrap.json
4. apt install libnss-extrausers
5. ln -s /var/lib/pam-nss-signedjit/passwd /var/lib/extrausers/passwd && ln -s /var/lib/pam-nss-signedjit/group /var/lib/extrausers/group
6. edit /etc/nsswitch.conf adding

   passwd:         compat extrausers
   group:          compat extrausers

7. Add the following to /etc/ssh/sshd_config:

AuthorizedKeysCommand /usr/local/bin/pam-nss-signedjit sshkey --username %u
AuthorizedKeysCommandUser nobody

8. Add a crontab entry * * * * * /usr/local/bin/pam-nss-signedjit update 2>/dev/null >/dev/null
9. Add a sudoers entry %jitadmins ALL=(ALL) NOPASSWD: ALL
10. Add a common-auth entry auth requisite pam_listfile.so item=user sense=allow file=/var/lib/pam-nss-signedjit/jitedusers onerr=fail
    • If you want separate break-glass allow list you can use [success=1 default=ignore] instead of requisite and a second pam_listfile.so line with requisite
11. Add a common-session entry session required pam_mkhomedir.so skel=/etc/skel/ umask=0022