Webhooks
Gitea supports webhooks for repository events. This can be configured in the settings page /:username/:reponame/settings/hooks by a repository admin. Webhooks can also be configured on a per-organization and whole system basis. All event pushes are POST requests. The methods currently supported are:

Gitea (can also be a GET request)
Gogs
Slack
Discord
Dingtalk
Telegram
Microsoft Teams
Feishu
Wechatwork
Packagist
Event information
warning
The secret field in the payload is deprecated as of Gitea 1.13.0 and will be removed in 1.14.0: https://github.com/go-gitea/gitea/issues/11755

The following is an example of event information that will be sent by Gitea to a Payload URL:

X-GitHub-Delivery: f6266f16-1bf3-46a5-9ea4-602e06ead473
X-GitHub-Event: push
X-Gogs-Delivery: f6266f16-1bf3-46a5-9ea4-602e06ead473
X-Gogs-Event: push
X-Gitea-Delivery: f6266f16-1bf3-46a5-9ea4-602e06ead473
X-Gitea-Event: push

{
  "secret": "3gEsCfjlV2ugRwgpU#w1*WaW*wa4NXgGmpCfkbG3",
  "ref": "refs/heads/develop",
  "before": "28e1879d029cb852e4844d9c718537df08844e03",
  "after": "bffeb74224043ba2feb48d137756c8a9331c449a",
  "compare_url": "http://localhost:3000/gitea/webhooks/compare/28e1879d029cb852e4844d9c718537df08844e03...bffeb74224043ba2feb48d137756c8a9331c449a",
  "commits": [
    {
      "id": "bffeb74224043ba2feb48d137756c8a9331c449a",
      "message": "Webhooks Yay!",
      "url": "http://localhost:3000/gitea/webhooks/commit/bffeb74224043ba2feb48d137756c8a9331c449a",
      "author": {
        "name": "Gitea",
        "email": "someone@gitea.io",
        "username": "gitea"
      },
      "committer": {
        "name": "Gitea",
        "email": "someone@gitea.io",
        "username": "gitea"
      },
      "timestamp": "2017-03-13T13:52:11-04:00"
    }
  ],
  "repository": {
    "id": 140,
    "owner": {
      "id": 1,
      "login": "gitea",
      "full_name": "Gitea",
      "email": "someone@gitea.io",
      "avatar_url": "https://localhost:3000/avatars/1",
      "username": "gitea"
    },
    "name": "webhooks",
    "full_name": "gitea/webhooks",
    "description": "",
    "private": false,
    "fork": false,
    "html_url": "http://localhost:3000/gitea/webhooks",
    "ssh_url": "ssh://gitea@localhost:2222/gitea/webhooks.git",
    "clone_url": "http://localhost:3000/gitea/webhooks.git",
    "website": "",
    "stars_count": 0,
    "forks_count": 1,
    "watchers_count": 1,
    "open_issues_count": 7,
    "default_branch": "master",
    "created_at": "2017-02-26T04:29:06-05:00",
    "updated_at": "2017-03-13T13:51:58-04:00"
  },
  "pusher": {
    "id": 1,
    "login": "gitea",
    "full_name": "Gitea",
    "email": "someone@gitea.io",
    "avatar_url": "https://localhost:3000/avatars/1",
    "username": "gitea"
  },
  "sender": {
    "id": 1,
    "login": "gitea",
    "full_name": "Gitea",
    "email": "someone@gitea.io",
    "avatar_url": "https://localhost:3000/avatars/1",
    "username": "gitea"
  }
}


Example
This is an example of how to use webhooks to run a php script upon push requests to the repository. In your repository Settings, under Webhooks, Setup a Gitea webhook as follows:

Target URL: http://mydomain.com/webhook.php
HTTP Method: POST
POST Content Type: application/json
Secret: 123
Trigger On: Push Events
Active: Checked
Now on your server create the php file webhook.php

<?php

$secret_key = '123';

// check for POST request
if ($_SERVER['REQUEST_METHOD'] != 'POST') {
    error_log('FAILED - not POST - '. $_SERVER['REQUEST_METHOD']);
    exit();
}

// get content type
$content_type = isset($_SERVER['CONTENT_TYPE']) ? strtolower(trim($_SERVER['CONTENT_TYPE'])) : '';

if ($content_type != 'application/json') {
    error_log('FAILED - not application/json - '. $content_type);
    exit();
}

// get payload
$payload = trim(file_get_contents("php://input"));

if (empty($payload)) {
    error_log('FAILED - no payload');
    exit();
}

// get header signature
$header_signature = isset($_SERVER['HTTP_X_GITEA_SIGNATURE']) ? $_SERVER['HTTP_X_GITEA_SIGNATURE'] : '';

if (empty($header_signature)) {
    error_log('FAILED - header signature missing');
    exit();
}

// calculate payload signature
$payload_signature = hash_hmac('sha256', $payload, $secret_key, false);

// check payload signature against header signature
if ($header_signature !== $payload_signature) {
    error_log('FAILED - payload signature');
    exit();
}

// convert json to array
$decoded = json_decode($payload, true);

// check for json decode errors
if (json_last_error() !== JSON_ERROR_NONE) {
    error_log('FAILED - json decode - '. json_last_error());
    exit();
}

// success, do something

There is a Test Delivery button in the webhook settings that allows to test the configuration as well as a list of the most Recent Deliveries.