new pregmatch for user function

func/main.sh

@@ -556,7 +556,8 @@ validate_format_email() {
 
 # Username
 validate_format_username() {
-    if ! [[ "$1" =~ ^[0-z]+(\.[0-z]+)?$ ]] || [[ "${#1}" -gt 28 ]]; then
+    if ! [[ "$1" =~ ^[a-zA-Z0-9]+(\.[a-zA-Z0-9]+)?$ ]] || [[ "${#1}" -gt 28 ]]
+        then
         echo "Error: $2 $1 is not valid"
         log_event "$E_INVALID" "$EVENT"
         exit $E_INVALID