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Very interesting project, I've been confronted with this kind of problem (managing SSH access for a large number of users) several times and don't think there's

Very interesting project, I've been confronted with this kind of problem (managing SSH access for a large number of users) several times and don't think there's a perfect solution for it yet. An alternative (but also imperfect) solution that I've relied on in the past is using certificate-based authentication: https://www.digitalocean.com/community/tutorials/how-to-create-an-ssh-ca-to-validate-hosts-and-clients-with-ubuntu https://www.digitalocean.com/community/tutorials/how-to-crea... This still requires the generation of certificates for users but it doesn't require updating the key material on the servers themselves. Having short-lived user certificates then gives the admin an easy way to revoke access to a server without changing any keys there by simply not issuing a new certificate to the user (and in urgent cases to also revoke the certificate as well before it expires, which requires intervention on the server though). I really hope that OpenSSH keeps improving their (still largely incomplete) PKI implementation, as I think it's a great feature for larger organizations.

mjlee 9y ago
I love vault's functionality around this: https://www.vaultproject.io/docs/secrets/ssh/signed-ssh-certificates.html https://www.vaultproject.io/docs/secrets/ssh/signed-ssh-cert... Along with something like Packer to bake the cert right into the image.
sz4kerto 9y ago
If you're managing large amount of servers and don't want to update configs on the servers themselves then use e.g. OpenLDAP.
- tr0ut 9y ago
  There is a security issue with using AD/OpenLDAP. That being passwords. An example is you can debug/trace the SSH process and see(log) passwords in clear text. Now of course this is both a trust and a escalated privilege issue. But a lot harder(impossible) with keys.
  - detaro 9y ago
    You can put keys in LDAP.
  - subway 9y ago
    If you're using straight passwords, sure, an ssh key (ideally in a directory) is going to beat a password-only login, but that ssh key is still subject to credential theft. I'm in the process of migrating an environment off of ssh-key authentication over to password+otp based kerberos (FreeIPA, though AD makes this easy too). A single password+otp login gets an 8 hour (non-renwable, in this environment) ticket. At the end of those 8 hours, users have to obtain another ticket with a password+otp. What's particularly nifty about this scheme is that it's useful for not only ssh access, but internal https services as well.
  - vertex-four 9y ago
    There's various methods to put SSH keys in LDAP. LDAP is an extensible database, so you can add a schema to attach SSH keys to a user (various schemas exist) - and the AuthorizedKeysCommand in your sshd_config can be hooked up to any program which can retrieve keys for a given user from anywhere (again, various programs exist). As an example already put together: https://github.com/jirutka/ssh-ldap-pubkey https://github.com/jirutka/ssh-ldap-pubkey
snuxoll 9y ago
FreeIPA - I wish more people knew about this. You can tie a public SSH key to a user (users can also self-register them) and it is automatically recognized on all hosts joined to the IPA domain, if you want to limit who has access to what the integrated RBAC facilities are there to handle that as well.
- chrisweekly 9y ago
  Cool! Thanks for the tip! :)
manigandham 9y ago
Have you looked at ScaleFT? https://www.scaleft.com https://www.scaleft.com They apply BeyondCorp style management for both server and web access. There is also Teleport by Gravitational: https://gravitational.com/teleport/ https://gravitational.com/teleport/
aren 9y ago
We (Foxpass, https://www.foxpass.com/ https://www.foxpass.com/) are a YCS15 company offering a SaaS (or on-prem) service to handle SSH key management & rotation, plus user and group management. With our API, some customers are creating dynamic access rules (for example, an on-caller might have 'sudo' during their on-call week, but not at other times). Like a hosted FreeIPA, but more powerful.

mjlee 9y ago

I love vault's functionality around this: https://www.vaultproject.io/docs/secrets/ssh/signed-ssh-certificates.html https://www.vaultproject.io/docs/secrets/ssh/signed-ssh-cert... Along with something like Packer to bake the cert right into the image.

sz4kerto 9y ago

If you're managing large amount of servers and don't want to update configs on the servers themselves then use e.g. OpenLDAP.

tr0ut 9y ago
There is a security issue with using AD/OpenLDAP. That being passwords. An example is you can debug/trace the SSH process and see(log) passwords in clear text. Now of course this is both a trust and a escalated privilege issue. But a lot harder(impossible) with keys.
- detaro 9y ago
  You can put keys in LDAP.
- subway 9y ago
  If you're using straight passwords, sure, an ssh key (ideally in a directory) is going to beat a password-only login, but that ssh key is still subject to credential theft. I'm in the process of migrating an environment off of ssh-key authentication over to password+otp based kerberos (FreeIPA, though AD makes this easy too). A single password+otp login gets an 8 hour (non-renwable, in this environment) ticket. At the end of those 8 hours, users have to obtain another ticket with a password+otp. What's particularly nifty about this scheme is that it's useful for not only ssh access, but internal https services as well.
- vertex-four 9y ago
  There's various methods to put SSH keys in LDAP. LDAP is an extensible database, so you can add a schema to attach SSH keys to a user (various schemas exist) - and the AuthorizedKeysCommand in your sshd_config can be hooked up to any program which can retrieve keys for a given user from anywhere (again, various programs exist). As an example already put together: https://github.com/jirutka/ssh-ldap-pubkey https://github.com/jirutka/ssh-ldap-pubkey

snuxoll 9y ago

FreeIPA - I wish more people knew about this. You can tie a public SSH key to a user (users can also self-register them) and it is automatically recognized on all hosts joined to the IPA domain, if you want to limit who has access to what the integrated RBAC facilities are there to handle that as well.

chrisweekly 9y ago
Cool! Thanks for the tip! :)

manigandham 9y ago

Have you looked at ScaleFT? https://www.scaleft.com https://www.scaleft.com They apply BeyondCorp style management for both server and web access. There is also Teleport by Gravitational: https://gravitational.com/teleport/ https://gravitational.com/teleport/

aren 9y ago

We (Foxpass, https://www.foxpass.com/ https://www.foxpass.com/) are a YCS15 company offering a SaaS (or on-prem) service to handle SSH key management & rotation, plus user and group management. With our API, some customers are creating dynamic access rules (for example, an on-caller might have 'sudo' during their on-call week, but not at other times). Like a hosted FreeIPA, but more powerful.