🌅 complete OS X keychain implementation.

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

credentials/helper.go

@@ -0,0 +1,15 @@
+package credentials
+
+// Credentials holds the information shared between docker and the credentials store.
+type Credentials struct {
+	ServerURL string
+	Username  string
+	Password  string
+}
+
+// Helper is the interface a credentials store helper must implement.
+type Helper interface {
+	Add(*Credentials) error
+	Delete(serverURL string) error
+	Get(serverURL string) (string, string, error)
+}