POST https://www.googleapis.com/blogger/v3/blogs/8070105920543249955/posts/
Authorization: /* OAuth 2.0 token here */
Content-Type: application/json

{
  "kind": "blogger#post",
  "blog": {
    "id": "8070105920543249955"
  },
  "title": "A new post",
  "content": "With <b>exciting</b> content..."
}

//main.php
$url = "https://accounts.google.com/o/oauth2/auth";
$params = array(
    "response_type" => 'code',
    "client_id" => '<AUTH_ID>.apps.googleusercontent.com',
    "redirect_uri" => 'http://example.com/authCallback.php',
    "scope" => 'https://www.googleapis.com/auth/blogger');

$request_to = $url.'?'.http_build_query($params);
header("Location: ".$request_to);

//authCallback.php
if(isset($_GET['code'])) {
    // Get an access token
    $code = $_GET['code'];
    $url = 'https://accounts.google.com/o/oauth2/token';
    $apikey = '<API_KEY>';
    $blogId = '<BLOG_ID>';
    $params = array(
        "code" => $code,
        "client_id" => urlencode("<ID>.apps.googleusercontent.com"),
        "client_secret" => urlencode("<SECRET>"),
        "redirect_uri" => urlencode("http://example.com/authCallback.php"),
        "grant_type" => urlencode("authorization_code")
    );

        // HTTP query builder
        foreach($params as $key=>$value) {
            $fields .= $key.'='.$value.'&';
        }

        rtrim($fields, '&');
        $ch = curl_init();
        curl_setopt($ch, CURLOPT_URL, $url);
        curl_setopt($ch, CURLOPT_POST, TRUE);
        curl_setopt($ch, CURLOPT_POSTFIELDS, $fields);
        curl_setopt($ch, CURLOPT_SSL_VERIFYHOST, FALSE);
        curl_setopt($ch, CURLOPT_SSL_VERIFYPEER, FALSE);
        curl_setopt($ch, CURLOPT_RETURNTRANSFER, TRUE);
        curl_setopt($ch, CURLOPT_FOLLOWLOCATION, TRUE);
        $data = curl_exec($ch);
        curl_close($ch);
        $response = json_decode($data);
        $accessToken = $response->access_token;
}