Add Logout Callback Functionality

docs/configuring.md

@@ -90,3 +90,27 @@ url_for('simplelogin.login', next='http://myothersite.com/')
 You can use the `from werkzeug.security import check_password_hash, generate_password_hash` utilities to encrypt passwords.
 
 A working example is available in `manage.py` of [example app](https://github.com/flask-extensions/Flask-SimpleLogin/tree/main/example)
+
+## Registering Custom Logout Callback(s)
+
+You can define multiple custom logout callbacks to be executed after the user logs out using the `register_on_logout_callback` method:
+
+```python
+from flask import Flask
+from flask_simplelogin import SimpleLogin
+
+app = Flask(__name__)
+app.config['SECRET_KEY'] = 'something-secret'
+simple_login = SimpleLogin(app)
+
+def my_post_logout_callback():
+    print("User has logged out")
+
+def another_post_logout_callback():
+    print("Another action after logout")
+
+simple_login.register_on_logout_callback(my_post_logout_callback)
+simple_login.register_on_logout_callback(another_post_logout_callback)
+```
+
+The callbacks will be executed in the order they were registered.

flask_simplelogin/__init__.py

@@ -196,6 +196,7 @@ def __init__(self, app=None, login_checker=None, login_form=None, messages=None)
         self.app = None
         self._login_checker = login_checker or default_login_checker
         self._login_form = login_form or LoginForm
+        self.on_logout_callbacks = []
         if app is not None:
             self.init_app(
                 app=app,
@@ -348,7 +349,15 @@ def login(self):
 
         return render_template("login.html", form=form, next=destiny), ret_code
 
+    def register_on_logout_callback(self, callback):
+        """Register a callback to be called on logout"""
+        self.on_logout_callbacks.append(callback)
+
     def logout(self):
         session.clear()
         self.flash("logout")
+
+        for callback in self.on_logout_callbacks:
+            callback()
+
         return redirect(self.config.get("home_url", "/"))

tests/test_app.py

@@ -1,5 +1,5 @@
 from base64 import b64encode
-from unittest.mock import call
+from unittest.mock import call, Mock
 
 from flask import url_for
 
@@ -80,6 +80,13 @@ def test_is_logged_in_from_json_request(app, client):
 
 
 def test_logout(app, client, csrf_token_for):
+    callback1 = Mock()
+    callback2 = Mock()
+
+    simplelogin = app.extensions["simplelogin"]
+    simplelogin.register_on_logout_callback(callback1)
+    simplelogin.register_on_logout_callback(callback2)
+
     client.get(url_for("simplelogin.login"))
     assert not is_logged_in()
     client.post(
@@ -94,6 +101,9 @@ def test_logout(app, client, csrf_token_for):
     client.get(url_for("simplelogin.logout"))
     assert not is_logged_in()
 
+    callback1.assert_called_once()
+    callback2.assert_called_once()
+
 
 def test_flash(app, mocker):
     mock_flash = mocker.patch("flask_simplelogin.flash")