chore: update username regexp

api/v1/auth.go

@@ -22,7 +22,7 @@ import (
 )
 
 var (
-	usernameMatcher = regexp.MustCompile("^[a-z]([a-z0-9-]{1,30}[a-z0-9])?$")
+	usernameMatcher = regexp.MustCompile("^[a-z0-9]([a-z0-9-]{1,30}[a-z0-9])$")
 )
 
 type SignIn struct {

api/v2/user_service.go

@@ -23,7 +23,7 @@ import (
 )
 
 var (
-	usernameMatcher = regexp.MustCompile("^[a-z]([a-z0-9-]{1,30}[a-z0-9])?$")
+	usernameMatcher = regexp.MustCompile("^[a-z0-9]([a-z0-9-]{1,30}[a-z0-9])$")
 )
 
 type UserService struct {