kerberos

Vault Plugin: Kerberos Auth Backend

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

You can find binaries on the Release page.

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",
                  json={'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"
...

$ vault write sys/plugins/catalog/auth/kerberos sha_256="$(shasum -a 256 'vault-plugin-auth-kerberos' | cut -d ' ' -f1)" command="vault-plugin-auth-kerberos -client-cert server.crt -client-key server.key"

1. 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/

1. 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"

1. 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

1. 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

If you wish to work on this plugin, you'll first need Go installed on your machine.

For local dev first make sure Go is properly installed, including setting up a GOPATH. Next, clone this repository into $GOPATH/src/github.com/wintoncode/vault-plugin-auth-kerberos. You can then download any required build tools by bootstrapping your environment:

$ make bootstrap

To compile a development version of this plugin, run make or make dev. This will put the plugin binary in the bin and $GOPATH/bin folders. dev mode will only generate the binary for your platform and is faster:

$ make
$ make dev

Put the plugin binary 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"
...

Start a Vault server with this config file:

$ vault server -config=path/to/config.json ...
...

Once the server is started, register the plugin in the Vault server's plugin catalog:

$ vault write sys/plugins/catalog/kerberos \
        sha_256=<expected SHA256 Hex value of the plugin binary> \
        command="vault-plugin-auth-kerberos"
...
Success! Data written to: sys/plugins/catalog/kerberos

Note you should generate a new sha256 checksum if you have made changes to the plugin. Example using openssl:

openssl dgst -sha256 $GOPATH/vault-plugin-auth-kerberos
...
SHA256(.../go/bin/vault-plugin-auth-kerberos)= 896c13c0f5305daed381952a128322e02bc28a57d0c862a78cbc2ea66e8c6fa1

Enable the auth plugin backend using the Kerberos auth plugin:

$ vault auth-enable -plugin-name='kerberos' plugin
...

Successfully enabled 'plugin' at 'kerberos'!

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'