Keystone Federation Identity

转自 http://wsfdl.com/openstack/2016/01/14/Keystone-Federation-Identity.html

Keystone federation identity 涉及很多概念，安装配置复杂，官网的文档又不够清晰，下面 4 篇文章在安装配置方面阐述的非常详细。

• Configure Keystone to Keystone Federation
• Configure Keystone to Testshib Federation with SAML
• Configure Keystone federation with Kerberos
• Configure Keystone federation with multi-IDP

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1. Federation Identity 简介

关于 federation identity，维基百科的定义如下：

A federated identity is the means of linking a person's electronic identity and attributes, stored across multiple distinct identity management systems(IDM).

在多个认证管理系统互相信任的基础上，federation identity 允许多个认证管理系统联邦认证各个系统的用户身份。它最重要的一个功能就是实现单点登录(Single Sign On)，用户仅需认证一次，便可访问这些互相授信的资源。比如 A 公司员工需使用 AWS 公有云，出于安全考虑，不希望在 AWS 的 IAM 创建员工账户信息，通过 federation identity 打通二者之间的用户授权和认证，A 公司员工只需在本公司完成身份认证即可访问 AWS 资源。我们把 A 公司称之为 Identity Provider(IDP), AWS 称之为 Service Provider(SP)。

• Service Provider: 服务提供方，它只提供服务，依赖 Identity Provider 认证用户身份
• Identity Provider: 断言(assertion)方，用于认证用户身份
• Assertion Protocol: 认证(断言)协议，Service Provider 和 Identity Provider 完成认证用户身份所用的协议，常用有 SAML, OpenID, Oauth 等

以 SAML 协议为例，典型的认证流程分为 Redirect Bindings 和 Artifact/POST Bindings 两种。

Federation identity 具有以下优点：

• 支持 SSO 单点登录
• 避免向 Service Provider 暴露用户信息，提高安全性
• 避免用户注册多个账号，增加用户负担

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Keystone Federation 的原理

Federation identity 为 hybrid cloud 在用户管理层面提供了良好的解决方案。Keystone 从 Icehouse 开始逐步增加 federation identity 的功能，Icehouse 支持 Keystone 作为 Service Provider，Juno 版本新增了 Identity Provider，支持 SAML 和 OpenID 两种认证协议。OpenStack 作为云服务的解决方案，对外提供计算、存储和网络等服务，多数场景下 Keystone 常常作为服务端，对接其它的 Identity Provider，所以本节着重阐述 Service Provider 的原理和流程。首先先介绍 3 类重要的 API。

• Identity Provider API: /OS-FEDERATION/identity_providers
  管理 Keystone 信任的 Identity Providers。
• Protocol API: /OS-FEDERATION/identity_providers/{idp_id}/protocols
  管理 Keystone 和某个 Identity Provider 之间认证的协议，通常为 oidc(OpenID) 或 saml2(SAML)。

• Mapping API: /OS-FEDERATION/mappings
  管理 Identity Provider 里的用户和 Keystone 里的用户之间的映射规则，通过该 API，管理员可以管理 IDP 中用户访问 Service 的权限。比如 IDP 有用户 A，B，通过配置 mapping rule，可以允许 A 有权限而 B 无权限访问。

  

为了支持 Service Provider，Keystone 必须运行在 Apache HTTPD 上，mod-shibboleth 作为 apache plugin 支持 SAML 认证协议，完成了 Keystone 和 IDP 之间用户的身份认证，流程如下。

1. 用户访问 /OS-FEDERATION/identity_providers/{identity_provider}/protocols/{protocol}/auth，Apache 捕获该 URL 并触发 mod-shibboleth 重定向至外部的 Identity Provider。
2. 外部的 Identity Provider 认证用户的身份并把用户的某些身份信息返回给 Apache，Apache 再把信息传给 Keystone。
3. Keystone 根据 mapping rule 把判断用户是否有访问权限，如果有访问权限，返回一个 unscoped token。用户可拿 unscoped token 查看可用的 project 并生成 scoped token，进而访问 OpenStack 的 API。

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Configure Keystone as a Service Provider

本节开始介绍如何安装配置 Keystone to Keystone Federation，重点参考了 it-is-time-to-play-with-keystone-to-keystone-federation-in-kilo(原文存在 2 处配置错误，本文已给予纠正)。 我们有两个服务器，分别作为 SP 和 IDP，二者均需按照官网的手册安装 Keystone。

• Linux: Ubuntu 14.04 LTS
• OpenStack: Kilo

更新 keystone.conf 如下配置：

[auth]
methods = external,password,token,oauth1,saml2
saml2 = keystone.auth.plugins.mapped.Mapped

Apache 新增如下配置：

Listen 5000
Listen 35357

<VirtualHost *:5000>
    WSGIScriptAliasMatch ^(/v3/OS-FEDERATION/identity_providers/.*?/protocols/.*?/auth)$ /var/www/cgi-bin/keystone/main/$1
     ......
</VirtualHost>

<VirtualHost *:35357>
    WSGIScriptAliasMatch ^(/v3/OS-FEDERATION/identity_providers/.*?/protocols/.*?/auth)$ /var/www/cgi-bin/keystone/admin/$1
      ......
</VirtualHost>

<Location /Shibboleth.sso>
    SetHandler shib
</Location>

<LocationMatch /v3/OS-FEDERATION/identity_providers/.*?/protocols/saml2/auth>
    ShibRequestSetting requireSession 1
    AuthType shibboleth
    ShibExportAssertion Off
    Require valid-user
</LocationMatch>

安装 Shibboleth：

apt-get install libapache2-mod-shib2

更新 /etc/shibboleth/attribute-map.xml 的以下配置项：

<Attribute name="openstack_user" id="openstack_user"/>
<Attribute name="openstack_roles" id="openstack_roles"/>
<Attribute name="openstack_project" id="openstack_project"/>
<Attribute name="openstack_user_domain" id="openstack_user_domain"/>
<Attribute name="openstack_project_domain" id="openstack_project_domain"/>

更新 /etc/shibboleth/shibboleth2.xml 的以下配置项：

<SSO entityID="http://idp:5000/v3/OS-FEDERATION/saml2/idp">
    SAML2 SAML1
</SSO>

<MetadataProvider type="XML" uri="http://idp:5000/v3/OS-FEDERATION/saml2/metadata"/>

启动 shibboleth 并重启 apache：

shib-keygen
service apache2 restart

查看 shibboleth 是否正常运行

unbuntu@SP:~# a2enmod shib2
Module shib2 already enabled

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Configure Keystone as an Identity Provider

安装 xmlsec1 和 pysaml2：

sudo apt-get install xmlsec1
sudo pip install pysaml2

更新 keystone.conf 的如下配置：

[saml]
certfile=/etc/keystone/ssl/certs/ca.pem
keyfile=/etc/keystone/ssl/private/cakey.pem
idp_entity_id=http://idp:5000/v3/OS-FEDERATION/saml2/idp
idp_sso_endpoint=http://idp:5000/v3/OS-FEDERATION/saml2/sso
idp_metadata_path=/etc/keystone/keystone_idp_metadata.xml

生成 DIP 的 metadata 并重启 apache HTTPD：

keystone-manage saml_idp_metadata > /etc/keystone/keystone_idp_metadata.xml
service apache2 restart

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Test Keystone to Keystone federation

• 在 Service Provider 端执行以下脚本，创建 domain, group, mapping, idp, protocol 等。其中 idp 指向另外一个作为 Identity Provider 的 Keystone，protocol 采用了 saml2 协议，mapping 的规则为只要 IDP 中名为 bob 或者 acme 的用户都可通过认证，并且映射到 Service 端的 federated_user 用户上。

import os

from keystoneclient import session as ksc_session
from keystoneclient.auth.identity import v3
from keystoneclient.v3 import client as keystone_v3

try:
    # Used for creating the ADMIN user
    OS_PASSWORD = '123456'
    OS_USERNAME = 'admin'
    # This will vary according to the entity:
    # the IdP or the SP
    OS_AUTH_URL = 'http://sp:35357/v3'
    OS_PROJECT_NAME = 'admin'
    OS_DOMAIN_NAME = 'default'
except KeyError as e:
    raise SystemExit('%s environment variable not set.' % e)

def client_for_admin_user():
    auth = v3.Password(auth_url=OS_AUTH_URL,
                       username=OS_USERNAME,
                       password=OS_PASSWORD,
                       user_domain_name=OS_DOMAIN_NAME,
                       project_name=OS_PROJECT_NAME,
                       project_domain_name=OS_DOMAIN_NAME)
    session = ksc_session.Session(auth=auth)
    return keystone_v3.Client(session=session)

# Used to execute all admin actions
client = client_for_admin_user()

def create_domain(client, name):
    try:
         d = client.domains.create(name=name)
    except:
         d = client.domains.find(name=name)
    return d

def create_group(client, name, domain):
    try:
         g = client.groups.create(name=name, domain=domain)
    except:
         g = client.groups.find(name=name)
    return g

def create_role(client, name):
    try:
        r = client.roles.create(name=name)
    except:
        r = client.roles.find(name=name)
    return r

print('\nCreating domain1')
domain1 = create_domain(client, 'domain1')

print('\nCreating group1')
group1 = create_group(client, 'group1', domain1)

print('\nCreating role Member')
role1 = create_role(client, 'Member')

print('\nGrant role Member to group1 in domain1')
client.roles.grant(role1, group=group1, domain=domain1)

print('\nList group1 role assignments')
client.role_assignments.list(group=group1)

def create_mapping(client, mapping_id, rules):
    try:
        m = client.federation.mappings.create(
            mapping_id=mapping_id, rules=rules)
    except:
        m = client.federation.mappings.find(
            mapping_id=mapping_id)
    return m

print('\nCreating mapping')
rules = [
{
    "local": [
        {
            "user": {
                "name": "federated_user"
            },
            "group": {
                "id": group1.id
            }
        }
    ],
    "remote": [
        {
            "type": "openstack_user",
            "any_one_of": [
                "bob",
                "acme"
            ]
        }
    ]
}
]

mapping1 = create_mapping(client, mapping_id='keystone-idp-mapping', rules=rules)

def create_idp(client, id, remote_id):
    idp_ref = {'id': id,
               'remote_ids': [remote_id],
               'enabled': True}
    try:
        i = client.federation.identity_providers.create(**idp_ref)
    except:
        i = client.federation.identity_providers.find(id=id)
    return i

def create_protocol(client, protocol_id, idp, mapping):
    try:
        p = client.federation.protocols.create(protocol_id=protocol_id,
                                               identity_provider=idp,
                                               mapping=mapping)
    except:
        p = client.federation.protocols.find(protocol_id=protocol_id)
    return p

print('\nRegister keystone-idp')
idp1 = create_idp(client, id='keystone-idp',
                  remote_id='http://idp:5000/v3/OS-FEDERATION/saml2/idp')

print('\nRegister protocol')
protocol1 = create_protocol(client, protocol_id='saml2', idp=idp1,
                            mapping=mapping1)

在 IDP 端执行以下脚本，用户 bob 获得一个 unscoped token，可拿该 token 向 SP 获取 scope token 后访问 Service 端的资源。

import json
import os

import requests

from keystoneclient import session as ksc_session
from keystoneclient.auth.identity import v3
from keystoneclient.v3 import client as keystone_v3

class K2KClient(object):
    def __init__(self):
        self.sp_id = 'keystone-sp'
        self.auth_url = 'http://idp:35357/v3'
        self.project_id = '582df27a0db14149a6da375b31fce3df'
        self.username = 'bob'
        self.password = '123456'
        self.domain_id = 'default'

    def v3_authenticate(self):
        auth = v3.Password(auth_url=self.auth_url,
                           username=self.username,
                           password=self.password,
                           user_domain_id=self.domain_id,
                           project_id=self.project_id)
        self.session = ksc_session.Session(auth=auth, verify=False)
        self.session.auth.get_auth_ref(self.session)
        self.token = self.session.auth.get_token(self.session)
    def _generate_token_json(self):
        return {
            "auth": {
                "identity": {
                    "methods": [
                        "token"
                    ],
                    "token": {
                        "id": self.token
                    }
                },
                "scope": {
                    "service_provider": {
                        "id": self.sp_id
                    }
                }
            }
        }

    def _check_response(self, response):
        if not response.ok:
            raise Exception("Something went wrong, %s" % response.__dict__)

    def get_saml2_ecp_assertion(self):
        token = json.dumps(self._generate_token_json())
        url = self.auth_url + '/auth/OS-FEDERATION/saml2/ecp'
        r = self.session.post(url=url, data=token, verify=False)
        self._check_response(r)
        self.assertion = str(r.text)

    def _get_sp(self):
        url = self.auth_url + '/OS-FEDERATION/service_providers/' + self.sp_id
        r = self.session.get(url=url, verify=False)
        self._check_response(r)
        sp = json.loads(r.text)[u'service_provider']
        return sp

    def _handle_http_302_ecp_redirect(self, response, location, **kwargs):
        return self.session.get(location, authenticated=False, **kwargs)

    def exchange_assertion(self):
        """Send assertion to a Keystone SP and get token."""
        sp = self._get_sp()

        r = self.session.post(
            sp[u'sp_url'],
            headers={'Content-Type': 'application/vnd.paos+xml'},
            data=self.assertion,
            authenticated=False,
            redirect=False)

        self._check_response(r)

        r = self._handle_http_302_ecp_redirect(r, sp[u'auth_url'],
                                               headers={'Content-Type':
                                               'application/vnd.paos+xml'})
        self.fed_token_id = r.headers['X-Subject-Token']
        self.fed_token = r.text

    def list_federated_projects(self):
        url = 'http://sp:5000/v3/OS-FEDERATION/projects'
        headers = {'X-Auth-Token': self.fed_token_id}
        r = requests.get(url=url, headers=headers)
        self._check_response(r)
        return json.loads(str(r.text))

    def _get_scoped_token_json(self, project_id):
        return {
            "auth": {
                "identity": {
                    "methods": [
                        "token"
                    ],
                    "token": {
                        "id": self.fed_token_id
                    }
                },
                "scope": {
                    "project": {
                        "id": project_id
                    }
                }
            }
        }

    def scope_token(self, project_id):
        # project_id can be select from the list in the previous step
        token = json.dumps(self._get_scoped_token_json(project_id))
        url = 'http://sp:5000/v3/auth/tokens'
        headers = {'X-Auth-Token': self.fed_token_id,
                   'Content-Type': 'application/json'}
        r = requests.post(url=url, headers=headers, data=token,
                          verify=False)
        self._check_response(r)
        self.scoped_token_id = r.headers['X-Subject-Token']
        self.scoped_token = str(r.text)

def main():
    client = K2KClient()
    client.v3_authenticate()
    client.get_saml2_ecp_assertion()
    print('ECP wrapped SAML assertion: %s' % client.assertion)
    client.exchange_assertion()
    print('Unscoped token id: %s' % client.fed_token_id)

    # If you want to get a scope token, please ensure federated_user has a project
    # and uncommen below codes.
    '''
    projects = client.list_federated_projects()
    print('Federated projects: %s' % projects['projects'])
    project_id = projects['projects'][0]['id']
    project_name = projects['projects'][0]['name']
    client.scope_token(project_id)
    print('Scoped token of ' + project_name + ' : ' + client.scoped_token_id)
    '''

if __name__ == "__main__":
    main()

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Reference

1. https://developer.rackspace.com/blog/keystone-to-keystone-federation-with-openstack-ansible/
2. https://specs.openstack.org/openstack/keystone-specs/api/v3/identity-api-v3-os-federation-ext.html
3. http://blog.rodrigods.com/it-is-time-to-play-with-keystone-to-keystone-federation-in-kilo/
4. https://bigjools.wordpress.com/2015/05/22/saml-federation-with-openstack/