Allow using username as identifier

store/memory.go

@@ -51,9 +51,16 @@ func (s *MemoryStore) UpdateUser(u users.User) error {
 	return nil
 }
 
-func (s *MemoryStore) GetUser(id string) (users.User, error) {
-	u, ok := s.Users[id]
+func (s *MemoryStore) GetUser(identifier string) (users.User, error) {
+	u, ok := s.Users[identifier]
 	if !ok {
+		// Check if identifier is username
+		for _, u := range s.Users {
+			if u.Username == identifier {
+				return u, nil
+			}
+		}
+
 		return u, ErrNoSuchUser
 	}
 

store/store.go

@@ -6,5 +6,5 @@ type UserStore interface {
 	AddUser(users.User) error
 	DeleteUser(id string) error
 	UpdateUser(users.User) error
-	GetUser(id string) (users.User, error)
+	GetUser(identifier string) (users.User, error)
 }