gcp-wif-test/docs/vault-userpass.md

Requesting a client certificate from a remote Vault server with user and password authentication

This guide shows how an administrator configures the Vault userpass authentication method, and how a user logs in to a remote Vault server and gets a client certificate signed by the Vault CA.

Prerequisites

• The Vault PKI configured as described in step 1a of the main README.md: the pki_int mount and the wif-client role (vault_configure.sh).
• A Vault server reachable over HTTPS. The examples use https://vault.example.com:8200.
• vault and openssl on the workstation of the administrator and of the user.

The commands are written for bash.

1. Configure the authentication

Role: Administrator

Point the CLI at the server and authenticate with an administrator token:

export VAULT_ADDR=https://vault.example.com:8200
export VAULT_TOKEN=<admin-token>

1. Create a policy that allows signing certificate requests with the wif-client role and nothing else.
2. Enable the userpass authentication method.
3. Create the user and attach the policy. The token of the user is valid for 15 minutes and can be renewed up to 1 hour.

pki-client.hcl:

path "pki_int/sign/wif-client" {
  capabilities = ["update"]
}

vault policy write pki-client pki-client.hcl

vault auth enable userpass

read -r -s -p "Password: " PASSWORD; echo
printf '%s' "${PASSWORD}" | vault write auth/userpass/users/alice \
    password=- \
    token_policies=pki-client \
    token_ttl=15m \
    token_max_ttl=1h
unset PASSWORD

password=- makes the CLI read the password from standard input, so it does not appear in the process list or in the shell history.

Note: The wif-client role accepts any common name (allow_any_name=true). Every user with the pki-client policy can therefore request a certificate with any subject CN, including the CN that other users or workloads rely on as the WiF subject. Restrict the role (allowed_domains, allow_bare_domains, enforce_hostnames) when the users must not choose their CN freely.

2. Request a certificate

Role: User

1. Set the address of the Vault server. Set VAULT_CACERT as well when the server certificate is issued by a private CA.

   export VAULT_ADDR=https://vault.example.com:8200
   export VAULT_CACERT=/path/to/server-ca.pem
   

2. Log in. The CLI asks for the password and stores the token in the token helper file (~/.vault-token).

   vault login -method=userpass username=alice
   

3. Generate the client key and the CSR locally. The key is never sent to Vault.

   openssl req \
       -newkey rsa:4096 \
       -keyout client_key.pem \
       -noenc \
       -subj "/CN=test-client" \
       -out client.csr
   

4. Sign the CSR with the Vault CA.

   vault write -field=certificate pki_int/sign/wif-client \
       csr=@client.csr \
       common_name=test-client \
       ttl=8760h > client_cert.pem
   

5. Check the certificate.

   openssl x509 -in client_cert.pem -noout -subject -issuer -dates -ext extendedKeyUsage
   

6. Revoke the token when the work is done.

   vault token revoke -self
   

The user token can only sign with the wif-client role. Reading the role or any other path returns permission denied.

To avoid storing the token on disk, log in with -no-store -token-only and keep the token in the environment:

export VAULT_TOKEN=$(vault login -no-store -token-only -method=userpass username=alice)