add string method

Author: imtbkcat

auth/auth.go

@@ -76,6 +76,12 @@ func (role *RoleIdentity) Restore(ctx *RestoreCtx) error {
 	return nil
 }
 
+// String converts UserIdentity to the format user@host.
+func (role *RoleIdentity) String() string {
+	// TODO: Escape username and hostname.
+	return fmt.Sprintf("%s@%s", role.Username, role.Hostname)
+}
+
 // CheckScrambledPassword check scrambled password received from client.
 // The new authentication is performed in following manner:
 //   SERVER:  public_seed=create_random_string()