Various fixes in login sources (#10428) (#10429)

Co-authored-by: guillep2k <18600385+guillep2k@users.noreply.github.com>

models/user.go

@@ -18,6 +18,7 @@ import (
 	"image/png"
 	"os"
 	"path/filepath"
+	"regexp"
 	"strconv"
 	"strings"
 	"time"
@@ -87,6 +88,9 @@ var (
 
 	// ErrUnsupportedLoginType login source is unknown error
 	ErrUnsupportedLoginType = errors.New("Login source is unknown")
+
+	// Characters prohibited in a user name (anything except A-Za-z0-9_.-)
+	alphaDashDotPattern = regexp.MustCompile(`[^\w-\.]`)
 )
 
 // User represents the object of individual and member of organization.
@@ -870,6 +874,11 @@ func isUsableName(names, patterns []string, name string) error {
 
 // IsUsableUsername returns an error when a username is reserved
 func IsUsableUsername(name string) error {
+	// Validate username make sure it satisfies requirement.
+	if alphaDashDotPattern.MatchString(name) {
+		// Note: usually this error is normally caught up earlier in the UI
+		return ErrNameCharsNotAllowed{Name: name}
+	}
 	return isUsableName(reservedUsernames, reservedUserPatterns, name)
 }