#Upstream GCP Service Auth Policy

This policy allows you to delegate authentication and authorization to your gateway without writing any code on your origin service by adding a GCP Issued ID Token to outgoing header allowing the service to be secured with GCP IAM. This is a useful means of securing your origin server so that only your Zuplo gateway can make requests against it.

This policy works with GCP Identity Aware Proxy or services like Cloud Run that natively support IAM authorization.

We recommend reading the serviceAccountJson from environment variables (so it is not checked in to source control) using the $env(ENV_VAR) syntax.

For information on how Google's service based auth works see Authenticating for invocation

#Configuration

The configuration shows how to configure the policy in the 'policies.json' document.

{
  "name": "my-upstream-gcp-service-auth-inbound-policy",
  "policyType": "upstream-gcp-service-auth-inbound",
  "handler": {
    "export": "UpstreamGcpServiceAuthInboundPolicy",
    "module": "$import(@zuplo/runtime)",
    "options": {
      "audience": "https://my-service-a2ev-uc.a.run.app",
      "scopes": ["https://www.googleapis.com/auth/cloud-platform"],
      "serviceAccountJson": "$env(SERVICE_ACCOUNT_JSON)"
    }
  }
}

#Policy Configuration

• name <string> - The name of your policy instance. This is used as a reference in your routes.
• policyType <string> - The identifier of the policy. This is used by the Zuplo UI. Value should be upstream-gcp-service-auth-inbound.
• handler.export <string> - The name of the exported type. Value should be UpstreamGcpServiceAuthInboundPolicy.
• handler.module <string> - The module containing the policy. Value should be $import(@zuplo/runtime).
• handler.options <object> - The options for this policy. See Policy Options below.

#Policy Options

The options for this policy are specified below. All properties are optional unless specifically marked as required.

• audience <string> - The audience for the service to be called. This is typically the URL of your service endpoint like 'https://my-service-a2ev-uc.a.run.app'. If calling a Google API, leave this empty.
• scopes <string[]> - The scopes to grant the access token. See documentation for details. This is only set with calling a Google API. If calling a service like Cloud Run, etc. leave this empty.
• serviceAccountJson (required) <string> - The Google Service Account key in JSON format. Note you can load this from environment variables using the $env(ENV_VAR) syntax.
• tokenRetries <number> - The number of times to retry fetching the token in the event of a failure. Defaults to 3.
• expirationOffsetSeconds <number> - The number of seconds less than the token expiration to cache the token. Defaults to 300.
• useMemoryCacheOnly <boolean> - This is an advanced option that should only be used if you do not want to persist information in ZoneCache.

#Using the Policy

This policy requires a Google Service Account and key that will be used to identify the Zuplo API Gateway. Once this policy is configured you will need to configure your GCP backend to only accept authenticated requests.

#Create the GCP Service Account

The first thing you will need to do to use this policy is create a service account. You should create a unique service account for your Zuplo Gateway (i.e. zuplo-gateway).

Give the account permission to call any services you want to proxy with Zuplo.

Next, you will need to create the Service Account key (using the JSON format). The json file will download.

Next, in your Zuplo project, set the SERVICE_ACCOUNT_JSON environment variable as a secret with the value of the downloaded JSON document.

#Configure the Policy

There are multiple uses for this policy. The way you are using this policy dictate the configuration options that need to be set.

#Invoking Your GCP Services

When calling your own services like Cloud Run, authenticating using Identity Aware Proxy, or calling other services that you own, you will specify the audience property.

When using this policy, you need to set the audience to the appropriate value depending on the service you are using.

For backend's secured with Identity Aware Proxy, the value for audience should be the Client ID of your OAuth application.

For backend's using Cloud Run IAM , the value for audience should be the full URL of the Cloud Run instance.

An example configuration of this policy when calling Cloud Run is shown below.

{
  "name": "gcp-service-auth",
  "policyType": "upstream-gcp-service-auth-inbound-policy",
  "handler": {
    "module": "$import(@zuplo/runtime)",
    "export": "UpstreamGcpServiceAuthInboundPolicy",
    "options": {
      "audience": "https://my-app-1235.a.run.app",
      "serviceAccountJson": "$env(GCP_SERVICE_ACCOUNT)"
    }
  }
}

#Invoking Google APIs

When using this policy to directly invoke a Google API (i.e. executing a Workflow the scopes property must be set.

The scopes need to be set to the values each Google API call specifies. The way you can find the required scopes is usually to refer to Google's documentation. They typically have a section title Authorization scopes. The scopes will be in the format of a url. For example, https://www.googleapis.com/auth/cloud-platform.

An example configuration of this policy when calling a Google Cloud API is shown below.

{
  "name": "gcp-service-auth-gcloud-api",
  "policyType": "upstream-gcp-service-auth-inbound-policy",
  "handler": {
    "module": "$import(@zuplo/runtime)",
    "export": "UpstreamGcpServiceAuthInboundPolicy",
    "options": {
      "scopes": [
        "https://www.googleapis.com/auth/cloud-platform",
        "https://www.googleapis.com/auth/cloud-platform.read-only",
        "https://www.googleapis.com/auth/cloudplatformprojects",
        "https://www.googleapis.com/auth/cloudplatformprojects.readonly"
      ],
      "serviceAccountJson": "$env(GCP_SERVICE_ACCOUNT)"
    }
  }
}

Read more about how policies work