How to get an OAuth 2.0 token in PHP?

I need to connect to a REST API of a customer. The first step is to get an OAuth 2.0 access token. I got the following information from the customer:

• Login (I assume it’s the client_id)
• Password (I assume it’s the client_secret)
• The flow is password
• The regular API URL
• The Token API URL

I found code at http://tutorialspage.com/simple-oauth2-example-using-php-curl/ and changed it, just for testing, to this:

private function getToken() {

    $curl = curl_init();

    $params = array(
        CURLOPT_URL =>  self::API_TOKEN_URL,
        CURLOPT_RETURNTRANSFER => true,
        CURLOPT_MAXREDIRS => 10,
        CURLOPT_TIMEOUT => 30,
        CURLOPT_POST => 1,
        CURLOPT_NOBODY => false,
        CURLOPT_HTTPHEADER => array(
            "cache-control: no-cache",
            "content-type: application/x-www-form-urlencoded",
            "accept: *",
            "accept-encoding: gzip, deflate",
        ),
        CURLOPT_POSTFIELDS => array(
            'username' => urlencode('[e-mail]'),
            'password' => urlencode('123 and 4'),
            'grant_type' => 'password'
        )
    );

    curl_setopt_array($curl, $params);
    // test
      //curl_setopt($curl, CURLOPT_HTTPAUTH, CURLAUTH_BASIC);
      //curl_setopt($curl, CURLOPT_USERPWD, '[e-mail]'.':'.'123 and 4');

    $response = curl_exec($curl);
    $err = curl_error($curl);

    curl_close($curl);

    if ($err) {
        echo "cURL Error #01: " . $err;
    } else {
        $response = json_decode($response, true);
        if(array_key_exists("access_token", $response)) return $response;
        if(array_key_exists("error", $response)) echo $response["error_description"];
        echo "cURL Error #02: Something went wrong! Please contact admin.";
    }
}

I would expect to get a JSON response containing valid OAuth 2.0 access_token, but instead I get an error:

{"error":"unsupported_grant_type"}

How to change the code to make it work?

Edit: It works over the shell-curl on my mac:

  curl -i 
  -X POST 
  -H 'Content-Type: application/x-www-form-urlencoded' 
  -d 'grant_type=password&username=[e-mail]&password=123 and 4' 
  https://the-token-api-url.foo

Verbose Informations Curl (MacShell):

*   Trying <IP HOST>
* TCP_NODELAY set
* Connected to <DNS HOST> (<IP HOST>) port 443 (#0)
* ALPN, offering http/1.1
* Cipher selection: ALL:!EXPORT:!EXPORT40:!EXPORT56:!aNULL:!LOW:!RC4:@STRENGTH
* successfully set certificate verify locations:
*   CAfile: /opt/local/share/curl/curl-ca-bundle.crt
  CApath: none
* TLSv1.2 (OUT), TLS header, Certificate Status (22):
* TLSv1.2 (OUT), TLS handshake, Client hello (1):
* TLSv1.2 (IN), TLS handshake, Server hello (2):
* TLSv1.2 (IN), TLS handshake, Certificate (11):
* TLSv1.2 (IN), TLS handshake, Server key exchange (12):
* TLSv1.2 (IN), TLS handshake, Server finished (14):
* TLSv1.2 (OUT), TLS handshake, Client key exchange (16):
* TLSv1.2 (OUT), TLS change cipher, Client hello (1):
* TLSv1.2 (OUT), TLS handshake, Finished (20):
* TLSv1.2 (IN), TLS change cipher, Client hello (1):
* TLSv1.2 (IN), TLS handshake, Finished (20):
* SSL connection using TLSv1.2 / <something>
* ALPN, server did not agree to a protocol
* Server certificate:
*  subject: CN=<CN>
*  start date: <date>
*  expire date: <date>
*  subjectAltName: host "<DNS HOST>" matched cert's "<DNS HOST>"
*  issuer: C=US; O=Let's Encrypt; CN=Let's Encrypt Authority X3
*  SSL certificate verify ok.
> POST /<URI PART>/token HTTP/1.1
> Host: <DNS HOST>
> User-Agent: curl/7.58.0
> Accept: */*
> Content-Type: application/x-www-form-urlencoded
> Content-Length: 73
> 
* upload completely sent off: 73 out of 73 bytes
< HTTP/1.1 200 OK
HTTP/1.1 200 OK
< Cache-Control: no-cache
Cache-Control: no-cache
< Pragma: no-cache
Pragma: no-cache
< Content-Type: application/json;charset=UTF-8
Content-Type: application/json;charset=UTF-8
< Expires: -1
Expires: -1
< Server: Microsoft-IIS/8.5
Server: Microsoft-IIS/8.5
< X-Powered-By: ASP.NET
X-Powered-By: ASP.NET
< Date: Tue, 05 Feb 2019 17:26:21 GMT
Date: Tue, 05 Feb 2019 17:26:21 GMT
< Content-Length: 671
Content-Length: 671

Verbose Informstions cURL PHP:

* Hostname in DNS cache was stale, zapped
*   Trying <IP>
* TCP_NODELAY set
* Connected to <DNS> (<IP>) port 443 (#0)
* ALPN, offering http/1.1
* Cipher selection: ALL:!EXPORT:!EXPORT40:!EXPORT56:!aNULL:!LOW:!RC4:@STRENGTH
* successfully set certificate verify locations:
*   CAfile: /opt/local/share/curl/curl-ca-bundle.crt
  CApath: none
* SSL connection using TLSv1.2 / <something>
* ALPN, server did not agree to a protocol
* Server certificate:
*  subject: CN=<DNS>
*  start date: <date>
*  expire date: <date>
*  subjectAltName: host "<dns>" matched cert's "<dns>"
*  issuer: C=US; O=Let's Encrypt; CN=Let's Encrypt Authority X3
*  SSL certificate verify ok.
> POST /<uri part>/token HTTP/1.1
Host: <dns>
cache-control: no-cache
accept: *
accept-encoding: gzip, deflate
Content-Length: 384
Content-Type: application/x-www-form-urlencoded; boundary=------------------------<a hash>

< HTTP/1.1 400 Bad Request
< Cache-Control: no-cache
< Pragma: no-cache
< Content-Type: application/json;charset=UTF-8
< Expires: -1
< Server: Microsoft-IIS/8.5
< X-Powered-By: ASP.NET
< Date: Tue, 05 Feb 2019 17:25:39 GMT
< Content-Length: 34
* HTTP error before end of send, stop sending
< 
* Closing connection 0

I didn’t find the problem.

Answer

OK, thanks to Helen it works now.

private function getToken(){
    $curl = curl_init();

    $params = [
        CURLOPT_URL =>  self::API_TOKEN_URL,
        CURLOPT_RETURNTRANSFER => true,
        CURLOPT_MAXREDIRS => 10,
        CURLOPT_TIMEOUT => 30,

        CURLOPT_POST => 1,
        CURLOPT_NOBODY => false,
        CURLOPT_HTTPHEADER => array(
            "cache-control: no-cache",
            "content-type: application/x-www-form-urlencoded",
            "accept: */*",
            "accept-encoding: gzip, deflate",
        ),
        CURLOPT_POSTFIELDS => "grant_type=password&username=[e-mail]&password=123and4"
    ];

    curl_setopt_array($curl, $params);
    $response = curl_exec($curl);

    curl_close($curl);
}

The Problem was solved as I entered the Post Data as String: CURLOPT_POSTFIELDS => "grant_type=password&username=[e-mail]&password=123and4" Instead of a array:

CURLOPT_POSTFIELDS => array(
            'username' => urlencode('[e-mail]'),
            'password' => urlencode('123and4'),
            'grant_type' => 'password'
        )

Thanks <3!