Vault Plugin: Kerberos Auth Backend

Details

This is a standalone backend plugin for use with Hashicorp Vault. This plugin allows for users to authenticate with Vault via Kerberos/SPNEGO.

Usage

Authentication

You can authenticate by posting a valid SPNEGO Negotiate header to /v1/auth/kerberos/login.

try:
    import kerberos
except:
    import winkerberos as kerberos
import requests

service = "HTTP@vault.domain"
rc, vc = kerberos.authGSSClientInit(service=service, mech_oid=kerberos.GSS_MECH_OID_SPNEGO)
kerberos.authGSSClientStep(vc, "")
kerberos_token = kerberos.authGSSClientResponse(vc)

r = requests.post("https://vault.domain:8200/v1/auth/kerberos/login",
                  headers={'authorization': 'Negotiate ' + kerberos_token})
print('Vault token:', r.json()['auth']['client_token'])

Configuration

1. Install and register the plugin.

Put the plugin binary (vault-plugin-auth-kerberos) into a location of your choice. This directory will be specified as the plugin_directory in the Vault config used to start the server.

plugin_directory = "path/to/plugin/directory"

$ SHA256=$(shasum -a 256 'vault-plugin-auth-kerberos' | cut -d ' ' -f2)
$ vault plugin register \
        -sha256=$SHA256 \
        -command="vault-plugin-auth-kerberos" \
        -client-cert server.crt -client-key server.key \
        auth kerberos

2. Enable the Kerberos auth method:

$ vault auth enable -passthrough-request-headers=Authorization -allowed-response-headers=www-authenticate kerberos
Success! Enabled kerberos auth method at: kerberos/

3. Use the /config endpoint to configure Kerberos.

Create a keytab for the kerberos plugin:

$ ktutil
ktutil:  addent -password -p your_service_account@REALM.COM -e aes256-cts -k 1
Password for your_service_account@REALM.COM:
ktutil:  list -e
slot KVNO Principal
---- ---- ---------------------------------------------------------------------
   1    1            your_service_account@REALM.COM (aes256-cts-hmac-sha1-96)
ktutil:  wkt vault.keytab

The KVNO (-k 1) should match the KVNO of the service account. An error will show in the vault logs if this is incorrect.

Different encryption types can also be added to the keytab, for example -e rc4-hmac with additional addent commands.

Then base64 encode it:

base64 vault.keytab > vault.keytab.base64

vault write auth/kerberos/config keytab=@vault.keytab.base64 service_account="your_service_account"

4. Add a SPNs (Service Principal Names) to your KDC for your service and service account. This should map the vault service to the account it is running as:

# for Windows/Active Directory
setspn.exe -U -S HTTP/vault.domain:8200 your_service_account
setspn.exe -U -S HTTP/vault.domain your_service_account

5. Configure LDAP backend to look up Vault policies. Configuration for LDAP is identical to the LDAP auth method, but writing to to the Kerberos endpoint:

vault write auth/kerberos/config/ldap @vault-config/auth/ldap/config
vault write auth/kerberos/groups/example-role @vault-config/auth/ldap/groups/example-role

In non-kerberos mode, the LDAP bind and lookup works via the user that is currently trying to authenticate. If you're running LDAP together with Kerberos you might want to set a binddn/bindpass in the ldap config.

Developing

To run a development environment through Docker, use:

make dev-env

This will:

• Build the current local plugin code
• Start Vault in a Docker container
• Start a local Samba container to function as the domain server
• Start a local joined container that can be used for login testing
• Output a number of variables for you to export in your working terminal

Note: Press CTRL+C in your make dev-env window when you'd like to stop and tear down your dev environment.

To begin testing in a separate window, after exporting the variables given in make dev-env:

VAULT_PLUGIN_SHA=$(openssl dgst -sha256 pkg/linux_amd64/vault-plugin-auth-kerberos|cut -d ' ' -f2)
vault write sys/plugins/catalog/auth/kerberos sha_256=${VAULT_PLUGIN_SHA} command="vault-plugin-auth-kerberos"
vault auth enable \
    -path=kerberos \
    -passthrough-request-headers=Authorization \
    -allowed-response-headers=www-authenticate \
    vault-plugin-auth-kerberos
vault write auth/kerberos/config \
    keytab=@vault_svc.keytab.base64 \
    service_account="vault_svc"
vault write auth/kerberos/config/ldap \
    binddn=${DOMAIN_VAULT_ACCOUNT}@${REALM_NAME} \
    bindpass=${DOMAIN_VAULT_PASS} \
    groupattr=sAMAccountName \
    groupdn="${DOMAIN_DN}" \
    groupfilter="(&(objectClass=group)(member:1.2.840.113556.1.4.1941:={{.UserDN}}))" \
    insecure_tls=true \
    starttls=true \
    userdn="CN=Users,${DOMAIN_DN}" \
    userattr=sAMAccountName \
    upndomain=${REALM_NAME} \
    url=ldaps://${SAMBA_CONTAINER:0:12}.${DNS_NAME}

To authenticate, first drop into a Docker container, then its Python shell:

docker exec -it $DOMAIN_JOINED_CONTAINER /bin/bash
python

Revisit the VAULT_CONTAINER_PREFIX outputted earlier, as you'll need it below:

prefix = '<insert VAULT_CONTAINER_PREFIX here>'
import kerberos
import requests

host = prefix + ".matrix.lan:8200"
service = "HTTP@{}".format(host)
rc, vc = kerberos.authGSSClientInit(service=service, mech_oid=kerberos.GSS_MECH_OID_SPNEGO)
kerberos.authGSSClientStep(vc, "")
kerberos_token = kerberos.authGSSClientResponse(vc)

r = requests.post("http://{}/v1/auth/kerberos/login".format(host),
                  headers={'Authorization': 'Negotiate ' + kerberos_token})
print('Vault token:', r.json()['auth']['client_token'])

Tests

If you are developing this plugin and want to verify it is still functioning (and you haven't broken anything else), we recommend running the tests.

To run the tests, invoke make test:

$ make test

You can also specify a TESTARGS variable to filter tests like so:

$ make test TESTARGS='--run=TestConfig'

Acceptance Tests

Acceptance tests requires a Vault Enterprise license to be provided through VAULT_LICENSE and the following tools to be installed:

• Docker
• jq
• bats

Run the acceptance tests:

$ make test-acceptance VAULT_LICENSE=<vault-license>

Contributors

1. Clone the repo
2. Make changes on a branch
3. Test changes
4. Submit a Pull Request to GitHub

Maintained with ❤️ by Hashicorp.

With thanks to the original creators of this plugin:

• wintoncode
• @ah-
• @sambott
• @roederja2
• @jcmturner
• @kristian-lesko