Added "_" to valid usernames

string_utils/string_utils.go

@@ -83,7 +83,7 @@ func IsAlphaNumericOrDash(str string) bool {
 }
 
 func IsValidUsername(str string) bool {
-	regex := regexp.MustCompile("^[a-zA-Z0-9-.@+]*$")
+	regex := regexp.MustCompile("^[a-zA-Z0-9-.@+_]*$")
 	return regex.MatchString(str)
 }