Example: html button to get contacts from Outlook/Live/Hotmail in Graph Outlook

callbak.php

<?php
// initiate cURL resource
$ch = curl_init();
// where you want to post data
$url = "https://login.microsoftonline.com/common/oauth2/v2.0/token";
curl_setopt($ch, CURLOPT_URL,$url);
// tell curl you want to post something
curl_setopt($ch, CURLOPT_POST, true);

// define what you want to post
curl_setopt($ch, CURLOPT_POSTFIELDS, http_build_query(array(
    'grant_type'=>'authorization_code',
    'code'=> $_GET['code'],
    'redirect_uri'=>'https://www.example.com/callbak.php',
    'client_id'=> 'YOUR_CLIENT_ID', //https://account.live.com/developers/applications/create
    'client_secret'=> 'YOUR_SECRET_PASS'
)));

// return the output in string format
curl_setopt($ch, CURLOPT_RETURNTRANSFER, true);

// execute post
$output = curl_exec ($ch);

// close the connection
curl_close ($ch);

// show output
$info = json_decode($output);

$curl_h = curl_init('https://graph.microsoft.com/v1.0/me/contacts');

curl_setopt($curl_h, CURLOPT_HTTPHEADER,
    array(
        "Authorization: Bearer $info->access_token",
    )
);

# do not output, but store to variable
curl_setopt($curl_h, CURLOPT_RETURNTRANSFER, true);

$response = curl_exec($curl_h);

print_r($response);

index.html

<a href="https://login.microsoftonline.com/common/oauth2/v2.0/authorize?
 state=some_random_string
 &scope=https%3A%2F%2Fgraph.microsoft.com%2Fcontacts.read
 &response_type=code&approval_prompt=auto
 &client_id=YOUR_CLIENT_ID
 &redirect_uri=https%3A%2F%2Fwww.example.com%2Fcallbak.php">Get contacts</a>