class App extends React.Component
{
    render()
    {
        return (
            <form>
                <h1>Авторизация</h1>
                <input type = "text" name userName placeholder = "Логин"/>
                <input type = "text" name Password placeholder = "Пароль"/>
                <button>Авторизоваться</button>
            </form>
            );
    }
}

    fetch('http://example.com',{
        method: "POST",
        body: JSON.stringify(userData),
        headers: {
            'Accept': 'application/json',
            'Content-Type': 'application/json'
        },
    }).then(response => {
        response.json().then(data =>{
            console.log("Successful" + data);
        })
    })