This is a pam module that will authenticate a user based on them having an ssh certificate in their ssh-agent signed by a specified ssh CA. This is meant for things that require authentication post-login, usually on a remote system. So you ssh to machineA and sshd authenticates you (probably using your ssh cert, because if you’re using it for this, you’re probably using it for sshd as well). At that point when you want to run a command that requires authentication (eg. sudo), you can use pam-ussh for authentication.
Works on linux and osx. BSD doesn’t work because go doesn’t (yet) support buildmode=c-shared on bsd.
Building:
clone the repo and run ‘make’
$ git clone github.com/uber/pam-ussh
...
$ make
mkdir -p /home/pmoody/tmp/pam-ussh/.go/src
GOPATH=/home/pmoody/tmp/pam-ussh/.go go get golang.org/x/crypto/ssh
GOPATH=/home/pmoody/tmp/pam-ussh/.go go get golang.org/x/crypto/ssh/agent
GOPATH=/home/pmoody/tmp/pam-ussh/.go go get github.com/stretchr/testify/require
GOPATH=/home/pmoody/tmp/pam-ussh/.go go test -cover
PASS
coverage: 71.8% of statements
ok _/home/pmoody/tmp/pam-ussh 0.205s
GOPATH=/home/pmoody/tmp/pam-ussh/.go go build -buildmode=c-shared -o pam_ussh.so
$
Usage:
put this pam module where ever pam modules live on your system, eg. /lib/security
add it as an authentication method, eg.
$ grep auth /etc/pam.d/sudo
auth [success=1 default=ignore] /lib/security/pam_ussh.so
auth requisite pam_deny.so
auth required pam_permit.so
Runtime configuration options:
ca_file – string, the path to your TrustedUserCAKeys file, default /etc/ssh/trusted_user_ca. This is the pubkey that signs your user certificates.
authorized_principals – string, comma separated list of authorized principals, default "". If set, the user needs to have a principal in this list in order to use this module. If this and authorized_principals_file are both set, only the last option listed is checked.
authorized_principals_file – string, path to an authorized_principals file, default "". If set, users need to have a principal listed in this file in order to use this module. If this and authorized_principals are both set, only the last option listed is checked.
group – string, default, "" If set, the user needs to be a member of this group in order to use this module.
Example configuration:
the following looks for a certificate on $SSH_AUTH_SOCK that have been signed by user_ca. Additionally, the user needs to have a principal on the certificate that’s listed in /etc/ssh/root_authorized_principals
auth [success=1 default=ignore] /lib/security/pam_ussh.so ca_file=/etc/ssh/user_ca authorized_principals_file=/etc/ssh/root_authorized_principals
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