Javascript Fetch not getting a response

Question

I'm invoking an authentication service via javascript fetch to get an access token. The service is a simple RESTful call. I can see the call is successful using fiddler (with a 200 response and json data). However the fetch response never seems to get invoked. Below is a snippet:

const AUTHBODY = `grant_type=password&username=${username}&password=${password}&scope=roles offline_access profile`
const AUTHHEADER = new Headers({'Content-Type': 'application/x-www-form-urlencoded'})

const CONFIG = {
    method: 'POST',
    headers: AUTHHEADER,
    body: AUTHBODY
}

fetch('http://localhost:23461/connect/token', CONFIG).then(function(response) {
    console.log('response = ' + response)
    return response.json()
}).then(function(json) {
    console.log('json data = ' + json)
    return json
}).catch(function(error) {
    console.log('error = ' + error)
})

When executing the fetch above none of the console.logs gets executed... seems to just hang. But fiddler tells otherwise. Any ideas?

Answer 1

You probably met with the CORS origin policy problem. To tackle this you need some rights to access the server side of your API. In particular, you need to add a line in the header of php or another server endpoint:

<?php
header('Access-Control-Allow-Origin: *');
//or
header('Access-Control-Allow-Origin: http://example.com');

// Reading JSON POST using PHP
$json = file_get_contents('php://input');
$jsonObj = json_decode($json);

// Use $jsonObj
print_r($jsonObj->message);

...
// End php
?>

Also, make sure NOT to have in the header of your server endpoint:

header("Access-Control-Allow-Credentials" : true);

Model of working fetch code with POST request is:

const data = {
        message: 'We send a message to the backend with fetch()'
    };
const endpoint = 'http://example.com/php/phpGetPost.php';

fetch(endpoint, {
    method: 'POST',
    body: JSON.stringify(data)
})
.then((resp) => resp.json())
.then(function(response) {
    console.info('fetch()', response);
    return response;
});