Add support for Windows credential manager.

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

wincred/wincred_windows.go

@@ -0,0 +1,43 @@
+package wincred
+
+import (
+	winc "github.com/danieljoos/wincred"
+	"github.com/docker/docker-credential-helpers/credentials"
+)
+
+type wincred struct{}
+
+// New creates a new wincred.
+func New() credentials.Helper {
+	return wincred{}
+}
+
+// Add adds new credentials to the windows credentials manager.
+func (h wincred) Add(creds *credentials.Credentials) error {
+	g := winc.NewGenericCredential(creds.ServerURL)
+	g.UserName = creds.Username
+	g.CredentialBlob = []byte(creds.Password)
+	g.Persist = winc.PersistLocalMachine
+	return g.Write()
+}
+
+// Delete removes credentials from the windows credentials manager.
+func (h wincred) Delete(serverURL string) error {
+	g, err := winc.GetGenericCredential(serverURL)
+	if g == nil {
+		return nil
+	}
+	if err != nil {
+		return err
+	}
+	return g.Delete()
+}
+
+// Get retrieves credentials from the windows credentials manager.
+func (h wincred) Get(serverURL string) (string, string, error) {
+	g, _ := winc.GetGenericCredential(serverURL)
+	if g == nil {
+		return "", "", credentials.ErrCredentialsNotFound
+	}
+	return g.UserName, string(g.CredentialBlob), nil
+}