Authentication

Scenarios

  1. Cluster nodes that are frequently rebuilt

    Default settings work well; machines do not float, and a per-client password is not required.

  2. NAT HOWTO

  • Build client records in advance with bcfg2-admin, setting a uuid for each new client.

  • Set the address attribute for each to the address of the NAT.

  • Optionally, set a per-client password for each, and set into secure mode.

    Note

    This will require the use of the uuid and password from each client, and will require that they come through the NAT address.

Building bcfg2.conf automatically

This is a Cheetah template that automatically constructs per-client bcfg2.conf from the per-client metadata:

[communication]
#if $self.metadata.uuid != None
user = $self.metadata.uuid
#end if
#if $self.metadata.password != None
password = $self.metadata.password
#else
password = my-password-foobat
#end if

[components]
bcfg2 = https://localhost:6789

In this setup, this will cause any clients that have uuids established to be set to use them in bcfg2.conf. It will also cause any clients with passwords set to use them instead of the global password.

How Authentication Works

  1. First, the client is associated with a client record. If the client specifies a uuid, it uses this instead of the results of a dns or address lookup.
  2. Next, the ip address is verified against the client record. If the address doesn’t match, then the client must be set to floating=’true’
  3. Finally, the password is verified. If the client is set to secure mode, the only its per-client password is accepted. If it is not set to secure mode, then either the global password or per-client password will be accepted

Failure during any of these stages results in authentication failure. Note that clients set into secure mode that do not have per-client passwords set will not be able to connect.

SSL Cert-based client authentication

SSL-based client authentication is supported. This requires several things:

  1. Certificate Authority (to sign all keys)
  2. Server key and cert signed by the CA
  3. Client key and cert signed by the CA

A variety of CAs can be used, but these keys can be simply generated using the following set of steps:

  1. Setup a CA

    http://www.flatmtn.com/article/setting-openssl-create-certificates

  2. Create keys for each client and server, signing them with the CA signing cert

    http://www.flatmtn.com/article/setting-ssl-certificates-apache

    Note

    The client CN must be the FQDN of the client (as returned by a reverse DNS lookup of the ip address. Otherwise, you will end up with an error message on the client that looks like:

    Server failure: Protocol Error: 401 Unauthorized
Failed to download probes from bcfg2
Server Failure

    You will also see an error message on the server that looks something like:

    cmssrv01 bcfg2-server[9785]: Got request for cmssrv115 from incorrect address 131.225.206.122
cmssrv01 bcfg2-server[9785]: Resolved to cmssrv115.fnal.gov

  3. Distribute the keys and certs to the appropriate locations

  4. Copy the ca cert to clients, so that the server can be authenticated

Clients authenticating themselves with a certificate will be authenticated that way first; clients can be setup to either authenticate solely with certs, use certs with a fallback to password, or password only. Also a bootstrap mode will be added shortly; this will allow a client to authenticate with a password its first time, requiring a certificate all subsequent times. This behavior can be controlled through the use of the auth attribute in Metadata/clients.xml:

<Clients>
  <Client name='testclient' auth='cert'/>
</Clients>

Allowed values are:

Auth Type Meaning
cert Certificates must be used
cert+password Certificate or password may be used. If a certificate is used, the password must also be used.
bootstrap Password can be used for one client run, after that only certificate is allowed

cert+password is the default. This can be changed by setting the authentication parameter in the [communication] section of bcfg2.conf. For instance, to set bootstrap mode as the global default, you would add the following to bcfg2.conf:

[communication]
authentication = bootstrap

bootstrap mode is currently incompatible with the Clients Database.