We can call HTTP service and get data from any remote server and represent in servicenow service portal. Also we can call servicenow rest message to get the data and represent in service portal.

Use Get Method in Client Script

$http({
  method: 'GET',
  url: 'https://jsonplaceholder.typicode.com/todos/1'
}).then(function successCallback(response) {
    // this callback will be called asynchronously
    // when the response is available
  }, function errorCallback(response) {
    // called asynchronously if an error occurs
    // or server returns response with an error status.
  });

Use POST Method in Client Script

var req = {
 method: 'POST',
 url: 'http://example.com',
 headers: {
   'Content-Type': undefined
 },
 data: { test: 'test' }
}

$http(req).then(function(){
//success function
}, function(){
// error function
});