OIDC Token Proxy for GCP

A way to configure Prometheus to scrape services deployed to Google Cloud Platform (GCP) that require authentication (using Google-minted OpenID Connect ID Tokens).

TL;DR

# Cloud Run service
- job_name: "some-service-xxxxxxxxxx-xx"
  scheme: https
  oauth2:
    client_id: "anything"
    client_secret: "anything"
    token_url: "http://gcp-oidc-token-proxy:7777"
    endpoint_params:
      audience: https://some-service-xxxxxxxxxx-xx.a.run.app
  static_configs:
  - targets:
    - "some-service-xxxxxxxxxx-xx.a.run.app:443"
- job_name: "some-service-yyyyyyyyyy-yy"
  scheme: https
  oauth2:
    client_id: "anything"
    client_secret: "anything"
    token_url: "http://gcp-oidc-token-proxy:7777"
    endpoint_params:
      audience: https://some-service-yyyyyyyyyy-yy.a.run.app
  static_configs:
  - targets:
    - "some-service-yyyyyyyyyy-yy.a.run.app:443"

NOTE

• client_id and client_secret must be included but can be any string other than ""
• token_url is a reference to the endpoint of the GCP OIDC Token Proxy
• scopes is not required (and is mutually exclusive with audience)
• oauth2.endpoint_params is used to provide the proxy with an audience value
• For Cloud Run services, the identity token's audience must include scheme: (i.e. https:)

ToC

• Background
• Cloud Run service
• Service Account
• Run
  • Kubernetes
  • Docker Compose
  • Docker
  • Podman
• Prometheus

Background

Prometheus supports only TLS and OAuth2 for authenticating scrape targets. Unfortunately, the OAuth2 configuration is insufficiently flexible to permit using a Google Service Account as an identity and to mine ID Tokens with the Service Account. This 'sidecar' (thanks Levi Harrison for the suggestion in this comment thread) performs as a proxy, configured to run as a Google Service Account, that mints ID Tokens that can be used by Prometheus' OAuth2 config.

Thanks also to Salmaan for guidance navigating Google's seeming myriad of OAuth2 and ID token related libraries and for the short-circuit in using ID tokens as the Bearer value.

In what follows, I am using a Google [Cloud Run] service by way of example but the principle should extend to any service that supports Google ID tokens.

CAVEAT Because of the way that the sidecar intercepts Prometheus' OAuth processing and because Google require's that ID tokens contain an audience value that reflects the Cloud Run service URL and because these URLs are service-specific, unfortunately, one limitation of this solution is that each Cloud Run service requires its own Prometheus job_name.

• Deploy a Cloud Run service to be scraped
• Create Service Account
• Run this proxy
• Configure Prometheus to point at it
• Scrape e.g. Cloud Run services

Cloud Run service

You can use gcloud to grab a Cloud Run service's URL:

ENDPOINT=$(\
  gcloud run services describe ${NAME} \
  --project=${PROJECT} \
  --platform=managed \
  --region=${REGION} \
  --format="value(status.address.url)") && \
ENDPOINT=${ENDPOINT#https://} && \
echo ${ENDPOINT}

NOTE The protocol (scheme) (usually https) and the // are removed from the ENDPOINT value as this is not expected by Prometheus targets.

Service Account

PROJECT="[[YOUR-PROJECT-ID]]"
ACCOUNT="oidc-token-proxy"
EMAIL="${ACCOUNT}@${PROJECT}.iam.gserviceaccount.com"

gcloud iam service-accounts create ${ACCOUNT} \
--display-name="OIDC Token Proxy" \
--description="Used by Prometheus to authenticate GCP services" \
--project=${PROJECT}

gcloud iam service-accounts keys create ${PWD}/${ACCOUNT}.json \
--iam-account=${EMAIL} \
--project=${PROJECT}

# The Service Account is able to invoke Cloud Run services
# This value should be adjusted for other GCP services
# https://cloud.google.com/run/docs/reference/iam/roles
gcloud projects add-iam-policy-binding ${PROJECT} \
--member=serviceAccount:${EMAIL} \
--role=roles/run.invoker

Run

Kubernetes

There are 3 steps to deploy the solution to Kubernetes:

• Create Namespace
• Create ConfigMap for Prometheus' config
• Create Secret for Google Service Account
• Deploy Prometheus w/ gcp-oidc-token-proxy sidecar

NOTE gcp-oidc-token-proxy need not be deployed as a sidecar.

ACCOUNT="..."
ENDPOINT="..."

NAMESPACE="gcp-oidc-token-proxy"
CONFIG="prometheus"
SECRET="${ACCOUNT}"

kubectl create namespace ${NAMESPACE}

# File: prometheus.yml
# Update audience and target-url values to reflect the Cloud Run service URL
# References to gcp-oidc-token-proxy as a sidecar should remain as localhost
PROMETHEUS=$(mktemp)

sed \
--expression="s|some-service-xxxxxxxxxx-xx.a.run.app|${ENDPOINT}|g" \
${PWD}/prometheus.yml > ${PROMETHEUS}

kubectl create configmap ${CONFIG} \
--from-file=prometheus.yml=${PROMETHEUS} \
--namespace=${NAMESPACE}

kubectl create secret generic ${SECRET} \
--from-file=key.json=${PWD}/${ACCOUNT}.json \
--namespace=${NAMESPACE}

# File: deployment.yml
# Update the reference to the ConfigMap name
# Update the reference to the Secret name
DEPLOYMENT=$(mktemp)

sed \
--expression="s|name: CONFIG|name: ${CONFIG}|g" \
--expression="s|secretName: SECRET|secretName: ${SECRET}|g" \
${PWD}/kubernetes/deployment.yml > ${DEPLOYMENT}

kubectl create --filename=${DEPLOYMENT} \
--namespace=${NAMESPACE}

# Await
kubectl wait \
--for=condition=Available \
deployment/prometheus \
--timeout=60s \
--namespace=${NAMESPACE}

# Don't do this in production
# Expose Prometheus on localhost:9090 and the proxy on localhost:7777/metrics
kubectl port-forward deployment/prometheus \
--namespace=${NAMESPACE} \
9090:9090 \
7777:7777

Once the deployment completes, you should be able to browse Prometheus' UI on localhost:9090 and the OIDC Token Proxy's metrics on localhost:7777.

To check logs:

CONTAINER="prometheus" # Or "gcp-oidc-token-proxy"
kubectl logs deployment/prometheus \
--container=${CONTAINER} \
--namespace=${NAMESPACE}

When done:

kubectl delete namespace/${NAMESPACE}

Docker Compose

Ensure prometheus.yml reflects the correct Cloud Run service URL.

NOTE localhost values will work when using Docker Compose but it is better to use the services' internal DNS name. In this case, localhost:9090 becomes prometheus:9090 and the two occurrences of localhost:7777 should be replaced by gcp-oidc-token-proxy:7777:

ACCOUNT="..."
ENDPOINT="..."

# File: prometheus.yml
# Update audience and target-url values to reflect the Cloud Run service URL
# Use Docker Compose internal DNS name to the reference to the Prometheus service
# Use Docker Compose internal DNS name to reference the GCP OIDC Token Proxy service
PROMETHEUS=$(mktemp)

sed \
--expression="s|some-service-xxxxxxxxxx-xx.a.run.app|${ENDPOINT}|g" \
--expression="s|localhost:9090|prometheus:9090|g" \
--expression="s|localhost:7777|gcp-oidc-token-proxy:7777|g" \
${PWD}/prometheus.yml > ${PROMETHEUS}


# File: docker-compose.yml
# Update the reference to prometheus.yml with the value of the PROMETHEUS variable
# Update the reference to ACCOUNT with the value of the ACCOUNT variable
DOCKER_COMPOSE=$(mktemp)

sed \
--expression="s|\${PWD}/prometheus.yml|${PROMETHEUS}|g" \
--expression="s|ACCOUNT.json|${ACCOUNT}.json|g" \
${PWD}/docker-compose.yml > ${DOCKER_COMPOSE}

docker-compose --file=${DOCKER_COMPOSE} up

Once the services have been started, you should be able to browse Prometheus' UI on localhost:9090 and the OIDC Token Proxy's metrics on localhost:7777.

To check logs:

SERVICE="prometheus" # Or "gcp-oidc-token-proxy"
docker-compose logs ${SERVICE}

Docker

ACCOUNT="..."
ENDPOINT="..."

# File: prometheus.yml
# Update audience and target-url values to reflect the Cloud Run service URL
PROMETHEUS=$(mktemp)

sed \
--expression="s|some-service-xxxxxxxxxx-xx.a.run.app|${ENDPOINT}|g" \
${PWD}/prometheus.yml > ${PROMETHEUS}

docker run \
--detach --rm \
--name="prometheus" \
--net=host \
--publish=9090:9090 \
--volume=${PROMETHEUS}:/etc/prometheus/prometheus.yml \
docker.io/prom/prometheus:v2.30.2 \
  --config.file=/etc/prometheus/prometheus.yml \
  --web.enable-lifecycle

docker run \
--detach --rm \
--name="gcp-oidc-token-proxy" \
--publish=7777:7777 \
--volume=${PWD}/${ACCOUNT}.json:/secrets/key.json \
--env=GOOGLE_APPLICATION_CREDENTIALS=/secrets/key.json \
ghcr.io/dazwilkin/gcp-oidc-token-proxy:e3a90b5cffb6701341272a70261e81258b75afaa \
  --port=7777

Once the containers are running, you should be able to browse Prometheus' UI on localhost:9090 and the OIDC Token Proxy's metrics on localhost:7777.

To check logs:

NAME="prometheus" # Or "gcp-oidc-token-proxy"
docker logs ${NAME}

When done:

for NAME in "prometheus" "gcp-oidc-token-proxy"
do
  docker container stop ${NAME}
done

Podman

ACCOUNT="..."
ENDPOINT="..."

POD="foo"
SECRET="${ACCOUNT}"

podman secret create ${SECRET} ${PWD}/${ACCOUNT}.json

podman pod create \
--name=${POD} \
--publish=9091:9090 \
--publish=7776:7777

# File: prometheus.yml
# Update audience and target-url values to reflect the Cloud Run service URL
PROMETHEUS=$(mktemp)

# Important
chmod go+r ${PROMETHEUS}

sed \
--expression="s|some-service-xxxxxxxxxx-xx.a.run.app|${ENDPOINT}|g" \
${PWD}/prometheus.yml > ${PROMETHEUS}

# Prometheus
podman run \
--detach --rm --tty \
--pod=${POD} \
--name=prometheus \
--volume=${PROMETHEUS}:/etc/prometheus/prometheus.yml \
docker.io/prom/prometheus:v2.30.2 \
  --config.file=/etc/prometheus/prometheus.yml \
  --web.enable-lifecycle

# GCP OIDC Token Proxy
podman run \
--detach --rm \
--pod=${POD} \
--name=gcp-oidc-token-proxy \
--secret=${SECRET} \
--env=GOOGLE_APPLICATION_CREDENTIALS=/run/secrets/${SECRET} \
ghcr.io/dazwilkin/gcp-oidc-token-proxy:e3a90b5cffb6701341272a70261e81258b75afaa \
  --port=7777

Once the containers are running, you should be able to browse Prometheus' UI on localhost:9090 and the OIDC Token Proxy's metrics on localhost:7777.

To check logs:

NAME="prometheus" # Or "gcp-oidc-token-proxy"
podman container logs ${NAME}

When done:

podman pod stop ${POD} && \
podman pod rm ${POD}

podman secret rm ${SECRET}

Prometheus

The Prometheus configuration file (prometheus.yml) needs to include an [OAuth] section that points to the proxy.

# E.g. Cloud Run service
- job_name: "cloudrun-service"
  scheme: https
  oauth2:
    client_id: "anything"
    client_secret: "anything"
    token_url: "http://gcp-oidc-token-proxy:7777/"
    endpoint_params:
      # The audience value must include scheme: (e.g. https:)
      audience: "https://some-service-xxxxxxxxxx-xx.a.run.app"
  static_configs:
  - targets:
    # Port 443 is not strictly necessary here as the scheme is HTTPS and 443 is the default port
    - "some-service-xxxxxxxxxx-xx.a.run.app:443"

The proxy exports metrics too and these can be included:

# GCP OAuth Token Proxy
- job_name: "gcp-oidc-token-proxy"
  static_configs:
  - targets:
    - "gcp-oidc-token-proxy:7777"

Targets

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