I Want To Convert This Code In To c#

Question

Hellio Friends I Want To Convert This Code Into C# Please Help Me For This

Code : - 

 

var loginUrl = 'loginAPI';

var username = 'UserName' || ''

var lowercaseUsername = username && username.toLowerCase()

var password = 'Password' || ''

var body = {

username: lowercaseUsername,

password: password

};

body = JSON.stringify(body);

fetch(loginUrl, {

method: 'post',

headers: {

'content-type': 'application/json'

},

body: body

}).then(function (response) {

return response.json();

}).then(function (data) {

// alert(data.idToken);

document.getElementById('Token').innerHTML = data.idToken;

});