next-hop-self

Linux - AD Auth with SSSD

Gary Ossewaarde's photo
Gary Ossewaarde
·

2 min read

Here are some brief notes on authenticating Linux users with AD - including using SSH keys. All of this was done on Ubuntu 22.04.

  1. Install necessary packages: sudo apt install sssd-ad sssd-tools realmd adcli

  2. Join the domain: sudo realm join <domain name>

  3. Enable home directories with pam: sudo pam-auth-update --enable mkhomedir

  4. Configure SSSD. Note: the line "ldap_user_ssh_public_key = sshPublicKey" becomes important in a later step, but included for completeness of sssd.conf

    ```

    /etc/sssd/sssd.conf

    [sssd] domains = config_file_version = 2 services = nss, pam, sudo

    [domain/] default_shell = /bin/bash krb5_store_password_if_offline = True cache_credentials = True krb5_realm = realmd_tags = manages-system joined-with-adcli id_provider = ad fallback_homedir = /home/%u@%d ad_domain = use_fully_qualified_names = True ldap_id_mapping = True access_provider = ad ldap_user_ssh_public_key = sshPublicKey

[sudo]

    Then, restart sssd and test: `sudo systemctl sssd restart`

5. Configure sudo to allow sudo based on AD group:

visudo %linuxadmins@ ALL=(ALL) NOPASSWD:ALL


6. Store SSH Keys in AD. This is well explained by [this blog post](https://blog.laslabs.com/2016/08/storing-ssh-keys-in-active-directory/) and does need to be rehashed here. The value mapping I used is sshPublicKey, and this config line in sssd.conf is what you need:

ldap_user_ssh_public_key = sshPublicKey

    Also, you'll need the following in `/etc/sshd/sshd_config`:

AuthorizedKeysCommand /usr/bin/sss_ssh_authorizedkeys AuthorizedKeysCommandUser root

    Restart SSH server: `sudo systemctl sshd restart`. You can also test authorized keys are being pulled correctly with the following command:

sudo /usr/bin/sss_ssh_authorizedkeys ssh-rsa AAAAB3NzaC1yc2EAAAADAQABAAABgQDex2RUYI75nlIPRyx1CPUVJrNE58qRVGJoUf+/Oq2xWBxAKjoksXYdyvCvNBijr56SBj7Zhze+LWUynlBD+Lp1afPtKft0qeltm7N7E9PKaIKUClxuSMnNJ/+Hr28k8+vFQfY/sKHzUstbykBh575IVQGwvXsEIsD70zKjkyHEGkytsZqDk+N35gSC68mya86+CaXvWCMn3njNmdeiYoUfQbOjdVCtfd7oB7mCZOfO9MIPFIEqiyHkXVePuBd0uOO9DjIO+WhPNeMHK9B7loOgA5foeGMeFS/7Hrp+FsX7zOeJcOqzBgogRhvEx63aEFziH+/dEfJlvI/OBVdEyDdOyIl7vAsi3rrB8uHN40vrFcfcOgeKHys3LwMu+rib75unvq6l0dGQlytz5ZITOKsmprXvc= `` You may also need to clear the SSSD cache during the initial setup,sudo sss_cache -E`