Actually compare to users in database

postgres/userservice.go

@@ -21,6 +21,19 @@ func (s *UserService) User(id budgeteer.ID) (*budgeteer.User, error) {
 	return u, nil
 }
 
+// UserByUsername returns a user for a given username.
+func (s *UserService) UserByUsername(username string) (*budgeteer.User, error) {
+	u := &budgeteer.User{Email: username}
+	err := s.DB.Model(&u).
+		Where("email = ?", username).
+		Limit(1).
+		Select()
+	if err != nil {
+		return nil, err
+	}
+	return u, nil
+}
+
 // CreateUser saves a user to the DB
 func (s *UserService) CreateUser(user *budgeteer.User) error {
 	user.ID = s.IDGenerator.New()