[node operator] Read azure config from k8s secret

Signed-off-by: Malte Poll <mp@edgeless.systems>

operators/constellation-node-operator/internal/azure/client/config.go

@@ -0,0 +1,32 @@
+package client
+
+import (
+	"encoding/json"
+	"errors"
+
+	"github.com/spf13/afero"
+)
+
+// cloudConfig uses same format as azure cloud controller manager to share the same kubernetes secret.
+// this definition only contains the fields we need.
+// reference: https://cloud-provider-azure.sigs.k8s.io/install/configs/ .
+type cloudConfig struct {
+	TenantID       string `json:"tenantId,omitempty"`
+	SubscriptionID string `json:"subscriptionId,omitempty"`
+}
+
+// loadConfig loads the cloud config from the given path.
+func loadConfig(fs afero.Fs, path string) (*cloudConfig, error) {
+	rawConfig, err := afero.ReadFile(fs, path)
+	if err != nil {
+		return nil, err
+	}
+	var config cloudConfig
+	if err := json.Unmarshal(rawConfig, &config); err != nil {
+		return nil, err
+	}
+	if config.TenantID == "" || config.SubscriptionID == "" {
+		return nil, errors.New("invalid config: tenantId and subscriptionId are required")
+	}
+	return &config, nil
+}