307 lines
17 KiB
XML
307 lines
17 KiB
XML
<?xml version="1.0" encoding="UTF-8"?>
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<chapter xmlns:xi="http://www.w3.org/2001/XInclude"
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xmlns:xlink="http://www.w3.org/1999/xlink"
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xmlns="http://docbook.org/ns/docbook"
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xmlns:db="http://docbook.org/ns/docbook" version="5.0"
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xml:id="ch024_authentication">
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<?dbhtml stop-chunking?>
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<title>Identity</title>
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<para>The OpenStack Identity Service (Keystone) supports multiple
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methods of authentication, including username & password,
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LDAP, and external authentication methods. Upon successful
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authentication, The Identity Service provides the user with an
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authorization token used for subsequent service requests.</para>
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<para>Transport Layer Security TLS/SSL provides authentication
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between services and persons using X.509 certificates. Although
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the default mode for SSL is server-side only authentication,
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certificates may also be used for client authentication.</para>
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<section xml:id="ch024_authentication-idp195568">
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<title>Authentication</title>
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<section xml:id="ch024_authentication-idp196256">
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<title>Invalid Login Attempts</title>
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<para>The Identity Service does not provide a method to limit
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access to accounts after repeated unsuccessful login attempts.
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Repeated failed login attempts are likely brute-force attacks
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(Refer figure Attack-types). This is a more significant issue
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in Public clouds.</para>
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<para>Prevention is possible by using an external authentication
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system that blocks out an account after some configured number
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of failed login attempts. The account then may only be
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unlocked with further side-channel intervention.</para>
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<para>If prevention is not an option, detection can be used to
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mitigate damage.Detection involves frequent review of access
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control logs to identify unauthorized attempts to access
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accounts. Possible remediation would include reviewing the
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strength of the user password, or blocking the network source
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of the attack via firewall rules. Firewall rules on the
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keystone server that restrict the number of connections could
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be used to reduce the attack effectiveness, and thus dissuade
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the attacker.</para>
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<para>In addition, it is useful to examine account activity for
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unusual login times and suspicious actions, with possibly
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disable the account. Often times this approach is taken by
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credit card providers for fraud detection and alert.</para>
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</section>
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<section xml:id="ch024_authentication-idp241008">
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<title>Multi-factor Authentication</title>
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<para>Employ multi-factor authentication for network access to
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privileged user accounts. The Identity Service supports
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external authentication services through the Apache web server
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that can provide this functionality. Servers may also enforce
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client-side authentication using certificates.</para>
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<para>This recommendation provides insulation from brute force,
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social engineering, and both spear and mass phishing attacks
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that may compromise administrator passwords.</para>
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</section>
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</section>
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<section xml:id="ch024_authentication-idp243184">
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<title>Authentication Methods</title>
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<section xml:id="ch024_authentication-idp243824">
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<title>Internally Implemented Authentication Methods</title>
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<para>The Identity Service can store user credentials in an SQL
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Database, or may use an LDAP-compliant directory server. The
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Identity database may be separate from databases used by other
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OpenStack services to reduce the risk of a compromise of the
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stored credentials.</para>
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<para>When authentication is provided via username and password,
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the Identity Service does not enforce policies on password
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strength, expiration, or failed authentication attempts as
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recommended by NIST Special Publication 800-118 (draft).
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Organizations that desire to enforce stronger password
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policies should consider using Keystone Identity Service
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Extensions or external authentication services.</para>
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<para>LDAP simplifies integration of Identity authentication
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into an organization's existing directory service and user
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account management processes.</para>
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<para>Authentication and authorization policy in OpenStack may
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be delegated to an external LDAP server. A typical use case is
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an organization that seeks to deploy a private cloud and
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already has a database of employees, the users. This may be in
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an LDAP system. Using LDAP as a source of authority
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authentication, requests to Identity Service are delegated to
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the LDAP service, which will authorize or deny requests based
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on locally set policies. A token is generated on successful
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authentication.</para>
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<para>Note that if the LDAP system has attributes defined for
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the user such as admin, finance, HR etc, these must be mapped
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into roles and groups within Identity for use by the various
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OpenStack services. The <emphasis>etc/keystone.conf</emphasis>
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file provides the mapping from the LDAP attributes to Identity
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attributes.</para>
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<para>The Identity Service <emphasis role="bold">MUST
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NOT</emphasis> be allowed to write to LDAP services used for
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authentication outside of the OpenStack deployment as this
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would allow a sufficiently privileged keystone user to make
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changes to the LDAP directory. This would allow privilege
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escalation within the wider organization or facilitate
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unauthorized access to other information and resources. In
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such a deployment, user provisioning would be out of the realm
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of the OpenStack deployment.</para>
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<note>
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<para>There is an <link
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xlink:href="https://bugs.launchpad.net/ossn/+bug/1168252"
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>OpenStack Security Note (OSSN) regarding keystone.conf
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permissions</link>.</para>
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<para>There is an <link
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xlink:href="https://bugs.launchpad.net/ossn/+bug/1155566"
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>OpenStack Security Note (OSSN) regarding potential DoS
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attacks</link>.</para>
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</note>
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</section>
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<section xml:id="ch024_authentication-idp251520">
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<title>External Authentication Methods</title>
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<para>Organizations may desire to implement external
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authentication for compatibility with existing authentication
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services or to enforce stronger authentication policy
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requirements. Although passwords are the most common form of
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authentication, they can be compromised through numerous
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methods, including keystroke logging and password compromise.
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External authentication services can provide alternative forms
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of authentication that minimize the risk from weak
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passwords.</para>
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<para>These include:</para>
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<itemizedlist>
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<listitem>
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<para>Password Policy Enforcement: Requires user passwords
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to conform to minimum standards for length, diversity of
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characters, expiration, or failed login attempts.</para>
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</listitem>
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<listitem>
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<para>Multi-factor authentication: The authentication
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service requires the user to provide information based on
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something they have, such as a one-time password token or
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X.509 certificate, and something they know, such as a
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password.</para>
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</listitem>
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<listitem>
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<para>Kerberos</para>
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</listitem>
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</itemizedlist>
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</section>
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</section>
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<section xml:id="ch024_authentication-idp256832">
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<title>Authorization</title>
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<para>The Identity Service supports the notion of groups and
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roles. Users belong to groups. A group has a list of roles.
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OpenStack services reference the roles of the user attempting to
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access the service. The OpenStack policy enforcer middleware
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takes into consideration the policy rule associated with each
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resource and the user's group/roles and tenant association to
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determine if he/she has access to the requested resource.</para>
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<para>The Policy enforcement middleware enables fine-grained
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access control to OpenStack resources. Only admin users can
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provision new users and have access to various management
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functionality. The cloud tenant would be able to only spin up
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instances, attach volumes, etc.</para>
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<section xml:id="ch024_authentication-idp259168">
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<title>Establish Formal Access Control Policies</title>
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<para>Prior to configuring roles, groups, and users, document
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your required access control policies for the OpenStack
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installation. The policies should be consistent with any
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regulatory or legal requirements for the organization. Future
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modifications to access control configuration should be done
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consistently with the formal policies. The policies should
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include the conditions and processes for creating, deleting,
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disabling, and enabling accounts, and for assigning privileges
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to the accounts. Periodically review the policies and ensure
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that configuration is in compliance with approved
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policies.</para>
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</section>
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<section xml:id="ch024_authentication-idp261600">
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<title>Service Authorization</title>
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<para>As described in the <link
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xlink:href="http://docs.openstack.org/admin-guide-cloud/content/index.html"
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><citetitle>OpenStack Cloud Administrator
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Guide</citetitle></link>, cloud administrators must define
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a user for each service, with a role of Admin. This service
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user account provides the service with the authorization to
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authenticate users.</para>
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<para>The Compute and Object Storage services can be configured
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to use either the "tempAuth" file or Identity Service to store
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authentication information. The "tempAuth" solution MUST NOT
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be deployed in a production environment since it stores
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passwords in plain text.</para>
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<para>The Identity Service supports client authentication for
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SSL which may be enabled. SSL client authentication provides
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an additional authentication factor, in addition to the
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username / password, that provides greater reliability on user
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identification. It reduces the risk of unauthorized access
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when user names and passwords may be compromised. However,
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there is additional administrative overhead and cost to issue
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certificates to users that may not be feasible in every
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deployment.</para>
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<note>
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<para>We recommend that you use client authentication with SSL
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for the authentication of services to the Identity
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Service.</para>
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</note>
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<para>The cloud administrator should protect sensitive
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configuration files for unauthorized modification. This can be
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achieved with mandatory access control frameworks such as
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SELinux, including <literal>/etc/keystone.conf</literal> and
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X.509 certificates.</para>
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<para>For client authentication with SSL, you need to issue
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certificates. These certificates can be signed by an external
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authority or by the cloud administrator. OpenStack services by
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default check the signatures of certificates and connections
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fail if the signature cannot be checked. If the administrator
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uses self-signed certificates, the check might need to be
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disabled. To disable these certificates, set
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<code>insecure=False</code> in the
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<code>[filter:authtoken]</code> section in the
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<filename>/etc/nova/api.paste.ini</filename> file. This
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setting also disables certificates for other
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components.</para>
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</section>
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<section xml:id="ch024_authentication-idp267040">
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<title>Administrative Users</title>
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<para>We recommend that admin users authenticate using Identity
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Service and an external authentication service that supports
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2-factor authentication, such as a certificate. This reduces
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the risk from passwords that may be compromised. This
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recommendation is in compliance with NIST 800-53 IA-2(1)
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guidance in the use of multi factor authentication for network
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access to privileged accounts.</para>
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</section>
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<section xml:id="ch024_authentication-idp268960">
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<title>End Users</title>
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<para>The Identity Service can directly provide end-user
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authentication, or can be configured to use external
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authentication methods to conform to an organization's
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security policies and requirements.</para>
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</section>
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</section>
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<section xml:id="ch024_authentication-idp270544">
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<title>Policies</title>
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<para>Each OpenStack service has a policy file in json format,
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called <emphasis role="bold">policy.json</emphasis>. The policy
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file specifies rules, and the rule that governs each resource. A
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resource could be API access, the ability to attach to a volume,
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or to fire up instances.</para>
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<para>The policies can be updated by the cloud administrator to
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further control access to the various resources. The middleware
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could also be further customized. Note that your users must be
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assigned to groups/roles that you refer to in your
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policies.</para>
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<para>Below is a snippet of the Block Storage service policy.json
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file.</para>
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<programlisting language="json"><xi:include href="../common/samples/authentication.json" parse="text"/></programlisting>
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<para>Note the <emphasis role="bold">default</emphasis> rule
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specifies that the user must be either an admin or the owner of
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the volume. It essentially says only the owner of a volume or
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the admin may create/delete/update volumes. Certain other
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operations such as managing volume types are accessible only to
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admin users.</para>
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</section>
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<section xml:id="ch024_authentication-idp276176">
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<title>Tokens</title>
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<para>Once a user is authenticated, a token is generated and used
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internally in OpenStack for authorization and access. The
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default token <emphasis role="bold">lifespan</emphasis>
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is<emphasis role="bold"> 24 hours</emphasis>. It is
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recommended that this value be set lower but caution needs to be
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taken as some internal services will need sufficient time to
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complete their work. The cloud may not provide services if
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tokens expire too early. An example of this would be the time
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needed by the Compute Service to transfer a disk image onto the
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hypervisor for local caching.</para>
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<para>The following example shows a PKI token. Note that, in
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practice, the token id value is about 3500 bytes. We shorten it
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in this example.</para>
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<programlisting language="json"><xi:include href="../common/samples/token.json" parse="text"/></programlisting>
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<para>Note that the token is often passed within the structure of
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a larger context of an Identity Service response. These
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responses also provide a catalog of the various OpenStack
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services. Each service is listed with its name, access endpoints
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for internal, admin, and public access.</para>
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<para>The Identity Service supports token revocation. This
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manifests as an API to revoke a token, to list revoked tokens
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and individual OpenStack services that cache tokens to query for
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the revoked tokens and remove them from their cache and append
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the same to their list of cached revoked tokens.</para>
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</section>
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<section xml:id="ch024_authentication-idp287584">
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<title>Future</title>
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<para>Domains are high-level containers for projects, users and
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groups. As such, they can be used to centrally manage all
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Keystone-based identity components. With the introduction of
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account Domains, server, storage and other resources can now be
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logically grouped into multiple Projects (previously called
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Tenants) which can themselves be grouped under a master
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account-like container. In addition, multiple users can be
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managed within an account Domain and assigned roles that vary
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for each Project.</para>
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<para>Keystone's V3 API supports multiple domains. Users of
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different domains may be represented in different authentication
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backends and even have different attributes that must be mapped
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to a single set of roles and privileges, that are used in the
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policy definitions to access the various service
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resources.</para>
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<para>Where a rule may specify access to only admin users and
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users belonging to the tenant, the mapping may be trivial. In
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other scenarios the cloud administrator may need to approve the
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mapping routines per tenant.</para>
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</section>
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</chapter>
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