创建3个示例HTTP请求，将新用户添加到数据库中。
请求1：
POST /user HTTP/1.1 
Host: example.com
Content-Type: application/json
{
  "username": "newuser_123", 
  "email": "newuser_123@example.com",
  "password": "pa$$w0rd"
}

请求2：
PUT /user HTTP/1.1 
Host: example.com
Content-Type: application/json
{
  "username": "newuser_123", 
  "email": "newuser_123@example.com",
  "password": "pa$$w0rd"
}

请求3：
POST /user/add HTTP/1.1 
Host: example.com
Content-Type: application/json
{
  "username": "newuser_123", 
  "email": "newuser_123@example.com",
  "password": "pa$$w0rd"
}