Add support for Windows credential manager.

Signed-off-by: David Calavera <david.calavera@gmail.com>

wincred/wincred_windows_test.go

@@ -0,0 +1,45 @@
+package wincred
+
+import (
+	"testing"
+
+	"github.com/docker/docker-credential-helpers/credentials"
+)
+
+func TestWinCredHelper(t *testing.T) {
+	creds := &credentials.Credentials{
+		ServerURL: "https://foobar.docker.io:2376/v1",
+		Username:  "foobar",
+		Password:  "foobarbaz",
+	}
+
+	helper := New()
+	if err := helper.Add(creds); err != nil {
+		t.Fatal(err)
+	}
+
+	username, password, err := helper.Get(creds.ServerURL)
+	if err != nil {
+		t.Fatal(err)
+	}
+
+	if username != "foobar" {
+		t.Fatalf("expected %s, got %s\n", "foobar", username)
+	}
+
+	if password != "foobarbaz" {
+		t.Fatalf("expected %s, got %s\n", "foobarbaz", password)
+	}
+
+	if err := helper.Delete(creds.ServerURL); err != nil {
+		t.Fatal(err)
+	}
+}
+
+func TestMissingCredentials(t *testing.T) {
+	helper := New()
+	_, _, err := helper.Get("https://adsfasdf.wrewerwer.com/asdfsdddd")
+	if err != credentials.ErrCredentialsNotFound {
+		t.Fatalf("exptected ErrCredentialsNotFound, got %v", err)
+	}
+}