Vault Agent with PKI certificate rendering

vault-agent-pki

### Configure variables
These variables will be used for this snippet. Please substitute accordingly.
```bash
export RootCAName="root_ca"
export InterCAName="inter_ca"
export CommonName="hashidemos.io"
export InterCommonName="inter.hashidemos.io"
export Root_CA_ttl="730h"
export Inter_CA_ttl="350h"
export Cert_ttl="8h"
```

### PKI Secrets engine setup
```bash
## Go to working directory
mkdir -p /tmp/certs && cd /tmp/certs

# Mount Root CA and generate certs:
vault secrets disable ${RootCAName}
vault secrets enable -path ${RootCAName} pki
vault secrets tune -max-lease-ttl=${Root_CA_ttl} ${RootCAName}

# Generate Root key and certs
vault write -format=json ${RootCAName}/root/generate/internal \
common_name="${CommonName}" ttl=${Inter_CA_ttl} | tee \
>(jq -r .data.certificate > /tmp/certs/ca.pem) \
>(jq -r .data.issuing_ca > /tmp/certs/issuing_ca.pem)

# Mount Intermediate CA and generate CSR:
vault secrets disable ${InterCAName}
vault secrets enable -path ${InterCAName} pki
vault secrets tune -max-lease-ttl=${Inter_CA_ttl} ${InterCAName}

vault write -format=json ${InterCAName}/intermediate/generate/internal \
common_name="${CommonName}" ttl=${Inter_CA_ttl} | tee \
>(jq -r .data.csr > /tmp/certs/${InterCAName}.csr)

vault write -format=json ${RootCAName}/root/sign-intermediate \
csr=@/tmp/certs/${InterCAName}.csr \
common_name="${CommonName}" ttl=${CA_ttl} | tee \
>(jq -r .data.certificate > /tmp/certs/${InterCAName}.pem) \
>(jq -r .data.issuing_ca > /tmp/certs/${InterCAName}_issuing_ca.pem)

vault write ${InterCAName}/intermediate/set-signed certificate=@/tmp/certs/${InterCAName}.pem

# Write URLs
vault write ${InterCAName}/config/urls \
 issuing_certificates="http://127.0.0.1:8200/v1/${InterCAName}/ca" \
 crl_distribution_points="http://127.0.0.1:8200/v1/${InterCAName}/crl" \
 ocsp_servers="http://127.0.0.1:8200/v1/${InterCAName}/ocsp" 

# Generate certificate for dev.hashidemos.io domain:
role_name=app1
prefix=dev
vault write ${InterCAName}/roles/${role_name} \
    allowed_domains="${prefix}.${CommonName}" \
    allow_subdomains="true" \
    max_ttl=${Cert_ttl} \
    generate_lease=true

# Verify
vault read ${InterCAName}/roles/${role_name}

## Test

# Generate a certificate with lease
vault write ${InterCAName}/issue/${role_name} common_name=app1.${prefix}.${CommonName}

# Generate a certificate with no lease
vault write ${InterCAName}/roles/${role_name}-no-lease \
    allowed_domains="${prefix}.${CommonName}" \
    allow_subdomains="true" \
    max_ttl=${Cert_ttl}
    
vault write ${InterCAName}/issue/${role_name}-no-lease common_name=app1.${prefix}.${CommonName}
```

### AppRole and Vault Agent configuration
```bash
## Setup AppRole and policy
mkdir -p /tmp/certs
cat <<EOF > /tmp/certs/cert.policy
path "${InterCAName}/issue*" {
  capabilities = ["create","update"]
}
path "auth/token/renew" {
  capabilities = ["update"]
}
path "auth/token/renew-self" {
  capabilities = ["update"]
}
EOF

vault policy write cert-policy /tmp/certs/cert.policy
vault token create -policy=cert-policy

vault auth enable approle
vault write auth/approle/role/cert-role token_policies="cert-policy" secret_id_ttl=24h token_ttl=5m token_max_ttl=4h
vault read -format=json auth/approle/role/cert-role/role-id > role.json
vault write -format=json -f auth/approle/role/cert-role/secret-id > secretid.json
export ROLE_ID="$(cat role.json | jq -r .data.role_id )" && echo $ROLE_ID | tee roleid
export SECRET_ID="$(cat secretid.json | jq -r .data.secret_id )" && echo $SECRET_ID |tee secretid

## Test
export VAULT_TOKEN=$(vault write -format=json auth/approle/login role_id=$ROLE_ID secret_id=$SECRET_ID | jq -r .auth.client_token)
vault write -format=json ${InterCAName}/issue/${role_name} \
    common_name=app1.${prefix}.${CommonName} ttl=5m

## Write template files
# https://github.com/hashicorp/vault-k8s/issues/21
cat <<TPL > dynamic-cert.tpl
{{ with secret "${InterCAName}/issue/${role_name}" "common_name=nginx.${prefix}.${CommonName}" "ttl=5m" }}
{{ .Data.certificate }}
{{ end }}
TPL

## Vault Agent with a source and destination
cat <<EOF > vault-agent.hcl
pid_file = "./pidfile"

vault {
  address = "http://127.0.0.1:8200"
}

auto_auth {
  method {
    type = "approle"

    config = {
      role_id_file_path = "/tmp/certs/roleid"
      secret_id_file_path = "/tmp/certs/secretid"
    }
  }

  sink {
    type = "file"
    config = {
      path = "/tmp/certs/token"
    }
  }
}

template {
  source = "/tmp/certs/dynamic-cert.tpl"
  destination = "/tmp/certs/app-certs.txt"
}
EOF

vault agent -log-level debug -config=./vault-agent.hcl

## Vault Agent with contents
cat <<EOF > vault-agent-contents.hcl
pid_file = "./pidfile"

vault {
  address = "http://127.0.0.1:8200"
}

auto_auth {
  method {
    type = "approle"

    config = {
      role_id_file_path = "/tmp/certs/roleid"
      secret_id_file_path = "/tmp/certs/secretid"
    }
  }

  sink {
    type = "file"
    config = {
      path = "/tmp/certs/token"
    }
  }
}

# TLS SERVER CERTIFICATE
template {
  contents = "{{ with secret \"${InterCAName}/issue/${role_name}\" \"common_name=nginx.${prefix}.${CommonName}\" \"ttl=1m\" }}{{ .Data.certificate }}{{ end }}"
  destination = "/tmp/certs/nginx.${prefix}.${CommonName}.crt"
}

# TLS PRIVATE KEY
template {
  contents = "{{ with secret \"${InterCAName}/issue/${role_name}\" \"common_name=nginx.${prefix}.${CommonName}\" \"ttl=1m\" }} {{ .Data.private_key }}{{ end }}"
  destination = "/tmp/certs/nginx.${prefix}.${CommonName}.key"
}

# TLS CA CERTIFICATE
template {
  contents = "{{ with secret \"${InterCAName}/issue/${role_name}\" \"common_name=nginx.${prefix}.${CommonName}\" \"ttl=1m\" }} {{ .Data.issuing_ca }}{{ end }}"
  destination = "/tmp/certs/ca.crt"
}
EOF


vault agent -log-level debug -config=./vault-agent-contents.hcl