Judging by my online searches, I’m far from the first to ask the question, but I’m keft with holes in my understanding of Kerberos and how services can authenticate via Kerberos (keytab).

I’m switching from sec=sys to sec=krb5p and either way struggle with local services which must place files on an NFS share for backup purposes. Using sec=sys things just work but the uid/gid numbers get matched locally and this often worked fine (when local services used the same aid/gid. But this doesn’t scale well, so I’m looking for ways to deal with this.

One way is to create a user in FreeIPA with the name of the service (for example bhsvc for Nakivo backup), and then adjust the uid on the local server to the IPA issued one, which is quick. But requires finding any file with the old id and changing it to the new one, which can be time consuming.

As the nfs client is a 3CX server, which don’t do well when manually configured as 3CX treat them as appliances. (God forbid someone might want to centrally manage these beast…); I would prefer not to change the uid of the local system account (phonesystem) to an IPA assigned one.

Despite finding how to configure gssproxy, I don’t yet understand how a daemon running as a certain user is mapped to an SPN with related keytab. Creating an SPN in IPA is easy, but how does the nfs-client know that a local system account should use/fetch a keytab for a certain SPN?
I could just manually set the uid of the local user on the nfs server, but while this worked with sec=sys, I don’t think this works with sec=krb5. So an option is to revert to sec=system, but I’d prefer not to.

user@3cx04:~$ cat /etc/gssproxy/00-3cxpbx.conf

[service/3CXPBX]

mechs = krb5

cred_store = ccache:/var/lib/gssproxy/clients/krb5cc_3cxpbx

cred_store = client_keytab:/var/lib/gssproxy/clients/3cxpbx.keytab

cred_usage = initiate

euid = 998