google-group-sync

README

Google Group Sync

Google Workspace group membership resolver via HTTP API. Fetches group memberships for a given user email using the Google Admin SDK Directory API.

What it does

Exposes a single HTTP endpoint that resolves which Google Workspace groups a user belongs to. Designed to be called by other services (e.g., zitadel-rbac-mapper) that need group information for access control decisions.

This service has no knowledge of Zitadel — it's a pure Google Workspace utility.

API

Resolve groups

POST /groups
Content-Type: application/json

{"email": "user@example.com"}

Success response:

HTTP/1.1 200 OK
Content-Type: application/json

{"groups": ["admins@example.com", "developers@example.com"]}

Error response (RFC 9457 Problem Details):

HTTP/1.1 400 Bad Request
Content-Type: application/problem+json

{
  "type": "https://github.com/truvity/google-group-sync/problems/invalid-member-key",
  "title": "Invalid Member Key",
  "status": 400,
  "detail": "memberKey \"not-an-email\" is not a valid email address"
}

HTTP/1.1 502 Bad Gateway
Content-Type: application/problem+json

{
  "type": "https://github.com/truvity/google-group-sync/problems/google-api-error",
  "title": "Google API Error",
  "status": 502,
  "detail": "failed to list groups for user@example.com: googleapi: Error 403: Not Authorized"
}

Health check

GET /health → 200 OK

Architecture

[Any caller] → POST /groups → [google-group-sync] → [Google Admin SDK] → [Google Workspace]
                                       │
                                       └─ domain-wide delegation (service account + impersonation)

Deployment Modes

google-group-sync ships three binaries for three deployment scenarios:

Mode	Binary	Entry point	Use case
Standalone	google-group-sync	cmd/google-group-sync/	K8s Deployment, local dev, any long-running process
Lambda	bootstrap	cmd/google-group-sync-lambda/	Standalone AWS Lambda with LWA layer
Extension	google-group-sync	cmd/google-group-sync-extension/	Lambda Extension sidecar for other Lambdas

All three modes run the same HTTP server with the same API. The difference is lifecycle management and configuration prefix.

Mode 1: Standalone (K8s / local)

The default binary. Runs as a regular HTTP server with signal handling.

# Local development
export GOOGLE_ADMIN_EMAIL=admin@example.com
export GOOGLE_SA_KEY_FILE=/path/to/sa-key.json
./google-group-sync

# Kubernetes via Helm chart
helm install google-group-sync oci://ghcr.io/truvity/charts/google-group-sync \
  --set env.GOOGLE_ADMIN_EMAIL=admin@example.com \
  --set env.GOOGLE_SA_KEY_FILE=/etc/secrets/sa-key.json \
  --set secrets.saKeySecretName=google-sa-key

The chart creates a Deployment, Service, and ServiceAccount. Mount the SA key as a Kubernetes Secret volume.

Mode 2: Lambda (standalone function)

Runs as its own Lambda function behind Lambda Web Adapter (LWA). LWA translates Lambda invocation events into HTTP requests to localhost:PORT. The binary starts as a normal HTTP server — no Lambda SDK needed.

The Lambda binary optionally loads the SA key from AWS Secrets Manager at startup (via SA_KEY_SECRET_NAME env var), so the key doesn't need to be in Lambda environment variables.

aws lambda create-function \
  --function-name google-group-sync \
  --runtime provided.al2023 \
  --architectures arm64 \
  --handler bootstrap \
  --zip-file fileb://google-group-sync_lambda_v0.4.0_arm64.zip \
  --layers "arn:aws:lambda:eu-central-1:753240598075:layer:LambdaAdapterLayerArm64:24" \
  --environment "Variables={GOOGLE_ADMIN_EMAIL=admin@example.com,SA_KEY_SECRET_NAME=my/sa-key}"

A Pulumi example is available in deploy/example-lambda/.

Mode 3: Extension (sidecar for other Lambdas)

Runs as a Lambda Extension — a sidecar process inside another Lambda's execution environment. The host Lambda calls http://localhost:9090/groups to resolve group memberships without needing a separate Lambda invocation.

Key differences from standalone/Lambda modes:

• GGS_ prefix — All env vars use the GGS_ prefix to avoid collisions with the host Lambda's env vars (e.g., GGS_GOOGLE_ADMIN_EMAIL, GGS_PORT)
• Port 9090 — Default port avoids conflict with the host Lambda (which typically uses 8080)
• Health port disabled — GGS_HEALTH_PORT=0 by default (no separate health listener)
• Extensions API registration — Registers with the Lambda Extensions API at startup, calls /next to signal init complete
• Secrets Manager — Loads SA key from GGS_SA_KEY_SECRET_NAME

Deploy as a Lambda Layer. The extension ZIP wraps the binary in an extensions/ directory so Lambda places it at /opt/extensions/google-group-sync:

# Publish as a Layer
aws lambda publish-layer-version \
  --layer-name google-group-sync-extension \
  --zip-file fileb://google-group-sync_extension_v0.4.0_arm64.zip \
  --compatible-architectures arm64

# Add to host Lambda
aws lambda update-function-configuration \
  --function-name my-webhook \
  --layers "arn:aws:lambda:...:layer:google-group-sync-extension:1" \
  --environment "Variables={...,GGS_GOOGLE_ADMIN_EMAIL=admin@example.com,GGS_SA_KEY_SECRET_NAME=my/sa-key}"

The host Lambda then calls http://localhost:9090/groups with a JSON body.

Configuration

All configuration is via environment variables. No config files, no CLI flags beyond --help and --version.

Standalone / Lambda mode

Env var	Required	Default	Description
GOOGLE_ADMIN_EMAIL	Yes	—	Admin email for domain-wide delegation
GOOGLE_SA_KEY_JSON	Mutual excl.	—	Raw SA key JSON (Lambda / env-based)
GOOGLE_SA_KEY_FILE	Mutual excl.	—	Path to SA key file (K8s mounted Secret)
SA_KEY_SECRET_NAME	No	—	AWS Secrets Manager secret name (Lambda only)
PORT	No	8080	HTTP server port
HEALTH_PORT	No	7070	Health probe port (separate listener)
CACHE_TTL	No	5m	Group membership cache TTL (Go duration)
CACHE_MAX_SIZE	No	10000	Max cache entries (LRU eviction)
LOG_LEVEL	No	info	Log level: debug, info, warn, error
LOG_FORMAT	No	json	Log format: json, text

Extension mode (GGS_ prefix)

All env vars use the GGS_ prefix. The host Lambda's unprefixed vars are ignored.

Env var	Required	Default	Description
GGS_GOOGLE_ADMIN_EMAIL	Yes	—	Admin email for domain-wide delegation
GGS_GOOGLE_SA_KEY_JSON	Mutual excl.	—	Raw SA key JSON
GGS_GOOGLE_SA_KEY_FILE	Mutual excl.	—	Path to SA key file
GGS_SA_KEY_SECRET_NAME	No	—	AWS Secrets Manager secret name
GGS_PORT	No	9090	HTTP server port
GGS_HEALTH_PORT	No	0	Health probe port (0 = disabled)
GGS_CACHE_TTL	No	5m	Group membership cache TTL
GGS_CACHE_MAX_SIZE	No	10000	Max cache entries
GGS_LOG_LEVEL	No	info	Log level
GGS_LOG_FORMAT	No	json	Log format

SA key loading priority

1. *_GOOGLE_SA_KEY_JSON set → use directly
2. *_SA_KEY_SECRET_NAME set → load from Secrets Manager at startup, set *_GOOGLE_SA_KEY_JSON
3. *_GOOGLE_SA_KEY_FILE set → read from file at startup
4. None set → error at startup

GOOGLE_SA_KEY_JSON and GOOGLE_SA_KEY_FILE are mutually exclusive (error if both set).

Authentication

The binary itself performs no authentication. Auth is delegated to the platform layer:

Platform	Auth mechanism
AWS Lambda	Function URL with AWS_IAM auth type — caller must have lambda:InvokeFunctionUrl permission
Lambda Extension	Localhost-only (no network auth needed — same execution environment)
Kubernetes	NetworkPolicy + service mesh — only authorized pods can reach the service
API Gateway	Cognito authorizer, IAM auth, or API keys at the gateway level

This keeps the binary simple and lets each deployment model use its native auth story.

Artifacts

Each GitHub Release publishes:

Artifact	Format	Architecture	Description
google-group-sync_<version>_linux_amd64.tar.gz	tar.gz	amd64	Standalone binary (Linux)
google-group-sync_<version>_linux_arm64.tar.gz	tar.gz	arm64	Standalone binary (Linux)
google-group-sync_<version>_darwin_amd64.tar.gz	tar.gz	amd64	Standalone binary (macOS)
google-group-sync_<version>_darwin_arm64.tar.gz	tar.gz	arm64	Standalone binary (macOS)
google-group-sync_lambda_<version>_arm64.zip	zip	arm64	Lambda ZIP (bootstrap binary)
google-group-sync_extension_<version>_arm64.zip	zip	arm64	Extension ZIP (Layer)
ghcr.io/truvity/google-group-sync:<version>	OCI	multi-arch	Container image (distroless)
oci://ghcr.io/truvity/charts/google-group-sync	Helm	—	Helm chart

Development

devbox shell              # activate dev environment
just build                # build binary
just test                 # run unit tests
just lint                 # run linter
just test-integration     # run integration tests (requires real Google SA key)
just snapshot             # build snapshot release locally

Related repos

• truvity/zitadel-rbac-mapper — consumes this service for group-based RBAC in Zitadel
• truvity/zitadel-operator — K8s operator for Zitadel resources
• truvity/zitadel-notify-relay — Zitadel notification relay

License

MIT