Adding simple credentials interface

credentials.go

@@ -0,0 +1,17 @@
+package socks5
+
+// CredentialStore is used to support user/pass authentication
+type CredentialStore interface {
+	Valid(user, password string) bool
+}
+
+// StaticCredentials enables using a map directly as a credential store
+type StaticCredentials map[string]string
+
+func (s StaticCredentials) Valid(user, password string) bool {
+	pass, ok := s[user]
+	if !ok {
+		return false
+	}
+	return password == pass
+}