fix: Add restriction to username when signing up (#1203)

object/check.go

@@ -313,3 +313,21 @@ func CheckAccessPermission(userId string, application *Application) (bool, error
 	}
 	return allowed, err
 }
+
+func CheckUsername(name string) string {
+	if name == "" {
+		return "Empty username."
+	} else if len(name) > 39 {
+		return "Username is too long (maximum is 39 characters)."
+	}
+
+	// https://stackoverflow.com/questions/58726546/github-username-convention-using-regex
+	re, _ := regexp.Compile("^[a-zA-Z0-9]+(?:-[a-zA-Z0-9]+)*$")
+	if !re.MatchString(name) {
+		return fmt.Sprintf("The name '%s' may only contain alphanumeric characters or hyphens, "+
+			"cannot have multiple consecutive hyphens, "+
+			"and cannot begin or end with a hyphen.", name)
+	}
+
+	return ""
+}