External Authentication System

Salt's External Authentication System (eAuth) allows for Salt to pass through command authorization to any external authentication system, such as PAM or LDAP.

Note

eAuth using the PAM external auth system requires salt-master to be run as root as this system needs root access to check authentication.

External Authentication System Configuration

The external authentication system allows for specific users to be granted access to execute specific functions on specific minions. Access is configured in the master configuration file and uses the access control system:

external_auth:
  pam:
    thatch:
      - 'web*':
        - test.*
        - network.*
    steve:
      - .*

The above configuration allows the user thatch to execute functions in the test and network modules on the minions that match the web* target. User steve is given unrestricted access to minion commands.

Salt respects the current PAM configuration in place, and uses the 'login' service to authenticate.

Note

The PAM module does not allow authenticating as root.

Note

state.sls and state.highstate will return "Failed to authenticate!" if the request timeout is reached. Use -t flag to increase the timeout

To allow access to wheel modules or runner modules the following @ syntax must be used:

external_auth:
  pam:
    thatch:
      - '@wheel'   # to allow access to all wheel modules
      - '@runner'  # to allow access to all runner modules
      - '@jobs'    # to allow access to the jobs runner and/or wheel module

Note

The runner/wheel markup is different, since there are no minions to scope the acl to.

Note

Globs will not match wheel or runners! They must be explicitly allowed with @wheel or @runner.

Warning

All users that have external authentication privileges are allowed to run saltutil.findjob. Be aware that this could inadvertently expose some data such as minion IDs.

Matching syntax

The structure of the external_auth dictionary can take the following shapes. Function matches are regular expressions; minion matches are compound targets.

By user:

external_auth:
  <eauth backend>:
    <user or group%>:
      - <regex to match function>

By user, by minion:

external_auth:
  <eauth backend>:
    <user or group%>:
      <minion compound target>:
        - <regex to match function>

By user, by runner/wheel:

external_auth:
  <eauth backend>:
    <user or group%>:
      <@runner or @wheel>:
        - <regex to match function>

By user, by runner+wheel module:

external_auth:
  <eauth backend>:
    <user or group%>:
      <@module_name>:
        - <regex to match function without module_name>

Groups

To apply permissions to a group of users in an external authentication system, append a % to the ID:

external_auth:
  pam:
    admins%:
      - '*':
        - 'pkg.*'

Limiting by function arguments

Positional arguments or keyword arguments to functions can also be whitelisted.

New in version 2016.3.0.

external_auth:
  pam:
    my_user:
      - '*':
        - 'my_mod.*':
            args:
            - 'a.*'
            - 'b.*'
            kwargs:
              'kwa': 'kwa.*'
              'kwb': 'kwb'
      - '@runner':
        - 'runner_mod.*':
            args:
            - 'a.*'
            - 'b.*'
            kwargs:
              'kwa': 'kwa.*'
              'kwb': 'kwb'

The rules:

  1. The arguments values are matched as regexp.

  2. If arguments restrictions are specified the only matched are allowed.

  3. If an argument isn't specified any value is allowed.

  4. To skip an arg use "everything" regexp .*. I.e. if arg0 and arg2 should be limited but arg1 and other arguments could have any value use:

    args:
      - 'value0'
      - '.*'
      - 'value2'
    

Usage

The external authentication system can then be used from the command-line by any user on the same system as the master with the -a option:

$ salt -a pam web\* test.ping

The system will ask the user for the credentials required by the authentication system and then publish the command.

Tokens

With external authentication alone, the authentication credentials will be required with every call to Salt. This can be alleviated with Salt tokens.

Tokens are short term authorizations and can be easily created by just adding a -T option when authenticating:

$ salt -T -a pam web\* test.ping

Now a token will be created that has an expiration of 12 hours (by default). This token is stored in a file named salt_token in the active user's home directory.

Once the token is created, it is sent with all subsequent communications. User authentication does not need to be entered again until the token expires.

Token expiration time can be set in the Salt master config file.

LDAP and Active Directory

Note

LDAP usage requires that you have installed python-ldap.

Salt supports both user and group authentication for LDAP (and Active Directory accessed via its LDAP interface)

OpenLDAP and similar systems

LDAP configuration happens in the Salt master configuration file.

Server configuration values and their defaults:

# Server to auth against
auth.ldap.server: localhost

# Port to connect via
auth.ldap.port: 389

# Use TLS when connecting
auth.ldap.tls: False

# LDAP scope level, almost always 2
auth.ldap.scope: 2

# Server specified in URI format
auth.ldap.uri: ''    # Overrides .ldap.server, .ldap.port, .ldap.tls above

# Verify server's TLS certificate
auth.ldap.no_verify: False

# Bind to LDAP anonymously to determine group membership
# Active Directory does not allow anonymous binds without special configuration
# In addition, if auth.ldap.anonymous is True, empty bind passwords are not permitted.
auth.ldap.anonymous: False

# FOR TESTING ONLY, this is a VERY insecure setting.
# If this is True, the LDAP bind password will be ignored and
# access will be determined by group membership alone with
# the group memberships being retrieved via anonymous bind
auth.ldap.auth_by_group_membership_only: False

# Require authenticating user to be part of this Organizational Unit
# This can be blank if your LDAP schema does not use this kind of OU
auth.ldap.groupou: 'Groups'

# Object Class for groups.  An LDAP search will be done to find all groups of this
# class to which the authenticating user belongs.
auth.ldap.groupclass: 'posixGroup'

# Unique ID attribute name for the user
auth.ldap.accountattributename: 'memberUid'

# These are only for Active Directory
auth.ldap.activedirectory: False
auth.ldap.persontype: 'person'

auth.ldap.minion_stripdomains: []

# Redhat Identity Policy Audit
auth.ldap.freeipa: False

Authenticating to the LDAP Server

There are two phases to LDAP authentication. First, Salt authenticates to search for a users' Distinguished Name and group membership. The user it authenticates as in this phase is often a special LDAP system user with read-only access to the LDAP directory. After Salt searches the directory to determine the actual user's DN and groups, it re-authenticates as the user running the Salt commands.

If you are already aware of the structure of your DNs and permissions in your LDAP store are set such that users can look up their own group memberships, then the first and second users can be the same. To tell Salt this is the case, omit the auth.ldap.bindpw parameter. Note this is not the same thing as using an anonymous bind. Most LDAP servers will not permit anonymous bind, and as mentioned above, if auth.ldap.anonymous is False you cannot use an empty password.

You can template the binddn like this:

auth.ldap.basedn: dc=saltstack,dc=com
auth.ldap.binddn: uid={{ username }},cn=users,cn=accounts,dc=saltstack,dc=com

Salt will use the password entered on the salt command line in place of the bindpw.

To use two separate users, specify the LDAP lookup user in the binddn directive, and include a bindpw like so

auth.ldap.binddn: uid=ldaplookup,cn=sysaccounts,cn=etc,dc=saltstack,dc=com
auth.ldap.bindpw: mypassword

As mentioned before, Salt uses a filter to find the DN associated with a user. Salt substitutes the {{ username }} value for the username when querying LDAP

auth.ldap.filter: uid={{ username }}

Determining Group Memberships (OpenLDAP / non-Active Directory)

For OpenLDAP, to determine group membership, one can specify an OU that contains group data. This is prepended to the basedn to create a search path. Then the results are filtered against auth.ldap.groupclass, default posixGroup, and the account's 'name' attribute, memberUid by default.

auth.ldap.groupou: Groups

Note that as of 2017.7, auth.ldap.groupclass can refer to either a groupclass or an objectClass. For some LDAP servers (notably OpenLDAP without the memberOf overlay enabled) to determine group membership we need to know both the objectClass and the memberUid attributes. Usually for these servers you will want a auth.ldap.groupclass of posixGroup and an auth.ldap.groupattribute of memberUid.

LDAP servers with the memberOf overlay will have entries similar to auth.ldap.groupclass: person and auth.ldap.groupattribute: memberOf.

When using the ldap('DC=domain,DC=com') eauth operator, sometimes the records returned from LDAP or Active Directory have fully-qualified domain names attached, while minion IDs instead are simple hostnames. The parameter below allows the administrator to strip off a certain set of domain names so the hostnames looked up in the directory service can match the minion IDs.

auth.ldap.minion_stripdomains: ['.external.bigcorp.com', '.internal.bigcorp.com']

Determining Group Memberships (Active Directory)

Active Directory handles group membership differently, and does not utilize the groupou configuration variable. AD needs the following options in the master config:

auth.ldap.activedirectory: True
auth.ldap.filter: sAMAccountName={{username}}
auth.ldap.accountattributename: sAMAccountName
auth.ldap.groupclass: group
auth.ldap.persontype: person

To determine group membership in AD, the username and password that is entered when LDAP is requested as the eAuth mechanism on the command line is used to bind to AD's LDAP interface. If this fails, then it doesn't matter what groups the user belongs to, he or she is denied access. Next, the distinguishedName of the user is looked up with the following LDAP search:

(&(<value of auth.ldap.accountattributename>={{username}})
  (objectClass=<value of auth.ldap.persontype>)
)

This should return a distinguishedName that we can use to filter for group membership. Then the following LDAP query is executed:

(&(member=<distinguishedName from search above>)
  (objectClass=<value of auth.ldap.groupclass>)
)
external_auth:
  ldap:
    test_ldap_user:
        - '*':
            - test.ping

To configure a LDAP group, append a % to the ID:

external_auth:
  ldap:
    test_ldap_group%:
      - '*':
        - test.echo

In addition, if there are a set of computers in the directory service that should be part of the eAuth definition, they can be specified like this:

external_auth:
  ldap:
    test_ldap_group%:
      - ldap('DC=corp,DC=example,DC=com'):
        - test.echo

The string inside ldap() above is any valid LDAP/AD tree limiter. OU= in particular is permitted as long as it would return a list of computer objects.