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SeciossLink の OpenID Connect を step-ca の Provisioner として ssh 証明書を発行する

2022/03/02

事前準備

 

インストール https://smallstep.com/docs/step-ca/installation

wget --no-check-certificate -O step.tar.gz https://dl.step.sm/gh-release/cli/docs-ca-install/v0.18.1/step_linux_0.18.1_amd64.tar.gz
wget --no-check-certificate -O step-ca.tar.gz https://dl.step.sm/gh-release/certificates/docs-ca-install/v0.18.1/step-ca_linux_0.18.1_amd64.tar.gz
tar -xf step.tar.gz
tar -xf step-ca.tar.gz
cp step_0.18.1/bin/step /usr/bin
cp step-ca_0.18.1/bin/step-ca /usr/bin

テストユーザーの追加

[root@shu ~]# adduser alice

 

CA 初期化(ssh 機能有効)

[root@shu ~]# step ca init --ssh
✔ Deployment Type: Standalone
What would you like to name your new PKI?
✔ (e.g. Smallstep): stepcashu
What DNS names or IP addresses would you like to add to your new CA?
✔ (e.g. ca.smallstep.com[,1.1.1.1,etc.]): shu.dev.secioss.work
✔ (e.g. ca.smallstep.com[,1.1.1.1,etc.]): shu.dev.secioss.work
✔ (e.g. :443 or 127.0.0.1:443): :8443
What would you like to name the CA's first provisioner?
✔ (e.g. you@smallstep.com): shuu.shisen@secioss.co.jp
Choose a password for your CA keys and first provisioner.
✔ [leave empty and we'll generate one]: Passwd01

Generating root certificate... done!
Generating intermediate certificate... done!
Generating user and host SSH certificate signing keys... done!

✔ Root certificate: /root/.step/certs/root_ca.crt
✔ Root private key: /root/.step/secrets/root_ca_key
✔ Root fingerprint: f9d4355c7fee1ecc30da460b39877eb73a0b75191241b25622b11f6b7775674b
✔ Intermediate certificate: /root/.step/certs/intermediate_ca.crt
✔ Intermediate private key: /root/.step/secrets/intermediate_ca_key
✔ SSH user public key: /root/.step/certs/ssh_user_ca_key.pub
✔ SSH user private key: /root/.step/secrets/ssh_user_ca_key
✔ SSH host public key: /root/.step/certs/ssh_host_ca_key.pub
✔ SSH host private key: /root/.step/secrets/ssh_host_ca_key
✔ Database folder: /root/.step/db
✔ Templates folder: /root/.step/templates
✔ Default configuration: /root/.step/config/defaults.json
✔ Certificate Authority configuration: /root/.step/config/ca.json

Your PKI is ready to go. To generate certificates for individual services see 'step help ca'.

※ 初期化に 8443 を指定したので、8443 ポート開ける必要です

ファイル構成

[root@shu ~]# tree .step
.step
├── certs
│   ├── intermediate_ca.crt
│   ├── root_ca.crt
│   ├── ssh_host_ca_key.pub
│   └── ssh_user_ca_key.pub
├── config
│   ├── ca.json
│   └── defaults.json
├── db
├── secrets
│   ├── intermediate_ca_key
│   ├── root_ca_key
│   ├── ssh_host_ca_key
│   └── ssh_user_ca_key
└── templates
    └── ssh
        ├── ca.tpl
        ├── config.tpl
        ├── known_hosts.tpl
        ├── sshd_config.tpl
        ├── step_config.tpl
        └── step_includes.tpl

6 directories, 16 files

 

ssh 側設定(step-ca の証明書を利用する)

ユーザーCA証明書を信頼する Get your host to trust your SSH user CA

[root@shu ~]# step ssh config --roots > /root/.step/certs/ssh_user_ca_key.pub

サーバー証明書とキーを作成 Issue a certificate for your host

[root@shu ~]# step ssh certificate --host shu.dev.secioss.work ssh_host_ecdsa_key
✔ Provisioner: shuu.shisen@secioss.co.jp (JWK) [kid: EdbT3PawAZFq5iPkpS1czMB_-T1F-mMY1m46FwQMuNI]
Please enter the password to decrypt the provisioner key:
✔ CA: https://shu.dev.secioss.work:8443
Please enter the password to encrypt the private key:
✔ Private Key: ssh_host_ecdsa_key
✔ Public Key: ssh_host_ecdsa_key.pub
✔ Certificate: ssh_host_ecdsa_key-cert.pub
[root@shu ~]# mv ssh_host_ecdsa_key /etc/ssh/step_ssh_host_ecdsa_key
[root@shu ~]# mv ssh_host_ecdsa_key-cert.pub /etc/ssh/step_ssh_host_ecdsa_key-cert.pub
[root@shu ~]# mv ssh_host_ecdsa_key.pub /etc/ssh/step_ssh_host_ecdsa_key.pub

 

ssh 設定ファイルの変更

[root@shu ~]# vi /etc/ssh/sshd_config

信頼するユーザーCA証明書のキーを追記 Add following to SSHD configuration

# This is the CA's public key for authenticating user certificates:
TrustedUserCAKeys /root/.step/certs/ssh_user_ca_key.pub

サーバー証明書とキーを追記 Add following to SSHD configuration

HostCertificate /etc/ssh/step_ssh_host_ecdsa_key-cert.pub
HostKey /etc/ssh/step_ssh_host_ecdsa_key

ssh 設定ファイル変更後サービスを再起動

[root@shu ~]# systemctl restart sshd

ssh 用ホスト証明書を自動更新する Automate host key rotation

[root@shu ~]# cat <<EOF > /etc/cron.weekly/rotate-ssh-certificate
#!/bin/sh
export STEPPATH=/root/.step
cd /etc/ssh && step ssh renew step_ssh_host_ecdsa_key-cert.pub step_ssh_host_ecdsa_key --force 2> /dev/null
exit 0
EOF
chmod 755 /etc/cron.weekly/rotate-ssh-certificate
[root@shu ~]# ll /etc/cron.weekly/rotate-ssh-certificate
-rwxr-xr-x 1 root root 153  2月 28 18:11 /etc/cron.weekly/rotate-ssh-certificate

 

OIDC による SSO 対応

 

slink 側の対応

slinktest 側 シングルサインオン | OpenID Connect を登録

サービスID stepcashu-tests2.com
クライアントID NdLuYwC725NcUBrEj42x6o58q4Z7mn6W
クライアントシークレット※ secret
リダイレクトURI※ http://localhost:10000

※ サービス登録後、管理者または利用するユーザーに許可するサービスの追加とアクセスの権限が必要です

 

step-ca 側の対応

step-ca に Provisioner を手動で追加
※1 listenAddress のポートを開ける必要です
※2 enableSSHCA が必要です
※3 admins のユーザーは自分自身以外のユーザーが発行できます

    {
        "type": "OIDC",
        "name": "slinktest/winodws",
        "clientID": "NdLuYwC725NcUBrEj42x6o58q4Z7mn6W",
        "clientSecret": "secret",
        "configurationEndpoint": "https://slinktest.secioss.net/oidc/.well-known/openid-configuration",
        "listenAddress": "localhost:10000",
        "admins": ["admin@tests2.com", "test01@tests2.com"],
        "claims": {
            "enableSSHCA": true
        }
    }

step-ca サービスを再起動

[root@shu ~]# step-ca /root/.step/config/ca.json

 

Windows から ssh でサーバーへログイン

 

step をインストール

C:\>curl.exe -LO https://dl.step.sm/gh-release/cli/docs-cli-install/v0.18.2/step_windows_0.18.2_amd64.zip
C:\>Expand-Archive -LiteralPath .\step_windows_0.18.2_amd64.zip -DestinationPath .
C:\>step_0.18.2\bin\step.exe version

サービスマネージャーを起動し、

C:\>services.msc

「OpenSSH Authentication Agent」を起動する、そして ssh-agent を起動

C:\>ssh-agent

 

step-ca サーバーを指定

C:\step_0.18.2\bin>step ca bootstrap --ca-url shu.dev.secioss.work:8443
'step ca bootstrap' requires the '--fingerprint' flag

C:\step_0.18.2\bin>step ca bootstrap --ca-url shu.dev.secioss.work:8443 --fingerprint f9d4355c7fee1ecc30da460b39877eb73a0b75191241b25622b11f6b7775674b
The root certificate has been saved in C:\Users\shu\.step\certs\root_ca.crt.
The authority configuration has been saved in C:\Users\shu\.step\config\defaults.json.

 

step で SSO ログイン

参考 https://smallstep.com/blog/diy-single-sign-on-for-ssh/

step の ssh ログインコマンドを叩くと、Windows のデフォルトブラウザが自動的に立ち上がり、
slinktest のログイン画面が表示されます、ログイン後 OIDC の許可画面が表示され、許可すると Success 表示されるとログイン完成です。

C:\step_0.18.2\bin>step ssh login alice
✔ Provisioner: slinktest/windows (OIDC) [client: LfgqFL24j528oM5N77fGK5U2fsFxFys9]
Your default web browser has been opened to visit:

https://slinktest.secioss.net/oidc/authorize.php?client_id=LfgqFL24j528oM5N77fGK5U2fsFxFys9&code_challenge=4ANFtYzGrF_ujWhmUVhJYHjp83wo6uP_ebE6xs7saMs&code_challenge_method=S256&nonce=49e7fbb8f976e24d33db26c5e66ceb3971cec90c5c8634eb57c03f529bc8ede6&redirect_uri=http%3A%2F%2Flocalhost%3A10000&response_type=code&scope=openid+email&state=WyJYeZ077CKFY0rFpWmv56HU0pmgtvSO

✔ CA: https://shu.dev.secioss.work:8443
✔ SSH Agent: yes

ログイン後は、普通の ssh でログインコマンドでターゲットサーバーへログインできるようになります

C:\step_0.18.2\bin>ssh alice@shu.dev.secioss.work
Last login: Wed Mar  9 14:41:10 2022 from 192.168.163.8
[alice@shu ~]$ 

下記の設定を追加することで、上記と同等なことが実現できます

C:\user\shu.ssh\config

Match exec "step ssh check-host %h"
    ForwardAgent yes
    User  alice
    UserKnownHostsFile "C:\user\shu\.ssh\known_hosts"
    ProxyCommand step ssh proxycommand %r %h %p --provisioner "slinktest/winodws"
C:\step_0.18.2\bin> ssh shu.dev.secioss.work
✔ Provisioner: slinktest/windows (OIDC) [client: LfgqFL24j528oM5N77fGK5U2fsFxFys9]
Your default web browser has been opened to visit:

https://slinktest.secioss.net/oidc/authorize.php?client_id=LfgqFL24j528oM5N77fGK5U2fsFxFys9&code_challenge=eEiEh97M9Vgzq25TeMp71_3YYuTF9b_XVh9lLaytJP8&code_challenge_method=S256&nonce=6562d2350f61911ccf2ac6ae49756ac5ba856cd9c7f9ef2619f1693867f477f8&redirect_uri=http%3A%2F%2Flocalhost%3A10000&response_type=code&scope=openid+email&state=IAosgtabAVsGAfYeaeTrYlLGE4XGAfnQ

✔ CA: https://shu.dev.secioss.work:8443
Last login: Wed Mar  9 17:33:28 2022 from 192.168.163.8
[alice@shu ~]$
[alice@shu ~]$ exit
ログアウト
Connection to shu.dev.secioss.work closed.
C:\step_0.18.2\bin>

 

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