wip: account details from az and the token

internal/provider/azure/azure.go

@@ -36,10 +36,11 @@ var objectTypes = []provider.ObjectType{provider.TypeSecret, provider.TypeKey, p
 type Provider struct {
 	id, label string // "" for the single-account defaults
 
-	cred  azcore.TokenCredential
-	opts  options
-	subs  *armsubscriptions.Client
-	graph *armresourcegraph.Client
+	cred    azcore.TokenCredential
+	opts    options
+	account *accountDetails // nil for a service principal from AZURE_*
+	subs    *armsubscriptions.Client
+	graph   *armresourcegraph.Client
 
 	mu      sync.Mutex
 	vaults  map[string]*vaultClients // by vault URL