COTOHA API Portal の使用例です。

acess_token.php

#! /usr/bin/php
<?php
// ------------------------------------------------------------------
//	access_token.php
//
//						Feb/26/2020
//
// ------------------------------------------------------------------
include('Requests/library/Requests.php');
require_once './vendor/autoload.php';

fputs (STDERR,"*** 開始 ***\n");

Requests::register_autoloader();

$dotenv = Dotenv\Dotenv::createImmutable(__DIR__);
$dotenv->load();

$client_id = getenv("CLIENT_ID");
$client_secret = getenv("CLIENT_SECRET");
$url_base = getenv("DEVELOPER_API_BASE_URL");
$url_publish = getenv("ACCESS_TOKEN_PUBLISH_URL");

$data = array('grantType' => 'client_credentials','clientId' => $client_id,
		'clientSecret' => $client_secret);
$str_json = json_encode ($data);
$headers = array('Content-Type' => 'application/json');

$request = Requests::post($url_publish, $headers, $str_json);

var_dump($request->status_code);

print("-----------\n");
var_dump($request->body);
print("-----------\n");

$json_string = $request->body;
$dict_aa = json_decode ($json_string,true);
print($dict_aa["access_token"] . "\n");

fputs (STDERR,"*** 終了 ***\n");

// ------------------------------------------------------------------
?>

実行結果

$ ./acess_token.php
*** 開始 ***
int(201)
-----------
string(249) "
          {
            "access_token": "7Zj26srl557J3ffR********", 
            "token_type": "bearer",
            "expires_in": "86399" ,
            "scope": "" ,    
            "issued_at": "1582683782964"           
           }
        "
-----------
7Zj26srl557J3ffRGfbdWYAbCT8U
*** 終了 ***