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Allow using delegated IAM with Pod Workload Identity #425

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Allow using delegated IAM with Pod Workload Identity #425

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19 changes: 17 additions & 2 deletions auth/auth.go
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Original file line number Diff line number Diff line change
Expand Up @@ -167,10 +167,25 @@ func (c *Client) Token(ctx context.Context, cfg *config.MountConfig) (*oauth2.To
return idBindToken, nil
}

gcpSAResp, err := c.IAMClient.GenerateAccessToken(ctx, &credentialspb.GenerateAccessTokenRequest{
req := &credentialspb.GenerateAccessTokenRequest{
Name: fmt.Sprintf("projects/-/serviceAccounts/%s", gcpSA),
Scope: secretmanager.DefaultAuthScopes(),
}, gax.WithGRPCOptions(grpc.PerRPCCredentials(oauth.TokenSource{TokenSource: oauth2.StaticTokenSource(idBindToken)})))
}

if gcpSADelegates, ok := saResp.Annotations["iam.gke.io/gcp-service-account-delegates"]; ok {
var delegates []string
if err := json.Unmarshal([]byte(gcpSADelegates), &delegates); err != nil {
return nil, fmt.Errorf("unable to parse delegates annotation on SA: %w", err)
}

klog.V(5).InfoS("matched service account delegates", "service_account_delegates", delegates)

for _, delegate := range delegates {
req.Delegates = append(req.Delegates, fmt.Sprintf("projects/-/serviceAccounts/%s", delegate))
}
}

gcpSAResp, err := c.IAMClient.GenerateAccessToken(ctx, req, gax.WithGRPCOptions(grpc.PerRPCCredentials(oauth.TokenSource{TokenSource: oauth2.StaticTokenSource(idBindToken)})))
if err != nil {
return nil, fmt.Errorf("unable to fetch gcp service account token: %w", err)
}
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14 changes: 14 additions & 0 deletions docs/authentication.md
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Original file line number Diff line number Diff line change
Expand Up @@ -13,6 +13,20 @@ a Google authentication token using the Kubernetes Service Account [Workload
Identity](https://cloud.google.com/kubernetes-engine/docs/how-to/workload-identity)
annotations.

The `iam.gke.io/gcp-service-account-delegates` annotation can be used to [impersonate a chain of service accounts](https://cloud.google.com/iam/docs/create-short-lived-credentials-delegated) to be able to authenitcate as the service account in `iam.gke.io/gcp-service-account`.

```yaml
apiVersion: v1
kind: ServiceAccount
metadata:
annotations:
iam.gke.io/gcp-service-account: [email protected]
iam.gke.io/gcp-service-account-delegates: '["[email protected]"]'
...
```

In this case, the pod must have the permissions to authenticate as `[email protected]` and that service account must have the `roles/iam.serviceAccountTokenCreator` role granted on `[email protected]`.

## `provider-adc` - GCP Provider Identity

In the `SecretProviderClass` you can set
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