support etcd credentials in etcd plugin (#2442)

* support etcd credentials in etcd plugin

fixes #2441

* try to fix cleanup of authentication

test/etcd_credentials_test.go

@@ -0,0 +1,72 @@
+// +build etcd
+
+package test
+
+import (
+	"context"
+	"testing"
+)
+
+// uses some stuff from etcd_tests.go
+
+func TestEtcdCredentials(t *testing.T) {
+	corefile := `.:0 {
+    etcd skydns.test {
+        path /skydns
+    }
+}`
+
+	ex, _, _, err := CoreDNSServerAndPorts(corefile)
+	if err != nil {
+		t.Fatalf("Could not get CoreDNS serving instance: %s", err)
+	}
+	defer ex.Stop()
+
+	etc := etcdPlugin()
+	username := "root"
+	password := "password"
+	key := "foo"
+	value := "bar"
+
+	var ctx = context.TODO()
+
+	if _, err := etc.Client.Put(ctx, key, value); err != nil {
+		t.Errorf("Failed to put dummy value un etcd: %v", err)
+	}
+
+	if _, err := etc.Client.RoleAdd(ctx, "root"); err != nil {
+		t.Errorf("Failed to create root role: %s", err)
+	}
+	if _, err := etc.Client.UserAdd(ctx, username, password); err != nil {
+		t.Errorf("Failed to create user: %s", err)
+	}
+	if _, err := etc.Client.UserGrantRole(ctx, username, "root"); err != nil {
+		t.Errorf("Failed to assign role to root user: %v", err)
+	}
+	if _, err := etc.Client.AuthEnable(ctx); err != nil {
+		t.Errorf("Failed to enable authentication: %s", err)
+	}
+
+	etc2 := etcdPluginWithCredentials(username, password)
+
+	defer func() {
+		if _, err := etc2.Client.AuthDisable(ctx); err != nil {
+			t.Errorf("Fail to disable authentication: %v", err)
+		}
+	}()
+
+	resp, err := etc2.Client.Get(ctx, key)
+	if err != nil {
+		t.Errorf("Fail to retrieve value from etcd: %v", err)
+	}
+
+	if len(resp.Kvs) != 1 {
+		t.Errorf("Too many response found: %+v", resp)
+		return
+	}
+	actual := resp.Kvs[0].Value
+	expected := "bar"
+	if string(resp.Kvs[0].Value) != expected {
+		t.Errorf("Value doesn't match, expected:%s actual:%s", actual, expected)
+	}
+}