Support optional authentication methods

docs/extensions.rst

@@ -414,10 +414,25 @@ decorator::
 While running an authenticated request, the user object returned by the
 authenticaction function is accessible as ``request.g.current_user``.
 
+If an endpoint is intended to work with or without authentication, then it can
+be protected with the ``auth.optional`` decorator::
+
+    @app.route('/')
+    @auth.optional
+    async def index(request):
+        if g.current_user:
+            return f'Hello, {request.g.current_user}!'
+        else:
+            return 'Hello, anonymous user!'
+
+As shown in the example, a route can check ``g.current_user`` to determine if
+the user is authenticated or not.
+
 Token Authentication
 ^^^^^^^^^^^^^^^^^^^^
 
-To set up token authentication, create an instance of :class:`TokenAuth <microdot.auth.TokenAuth>`::
+To set up token authentication, create an instance of
+:class:`TokenAuth <microdot.auth.TokenAuth>`::
 
     from microdot.auth import TokenAuth
 
@@ -438,6 +453,16 @@ protect your routes::
     async def index(request):
         return f'Hello, {request.g.current_user}!'
 
+Optional authentication can also be used with tokens::
+
+    @app.route('/')
+    @auth.optional
+    async def index(request):
+        if g.current_user:
+            return f'Hello, {request.g.current_user}!'
+        else:
+            return 'Hello, anonymous user!'
+
 User Logins
 ~~~~~~~~~~~
 

src/microdot/auth.py

@@ -36,6 +36,24 @@ class BaseAuth:
 
         return wrapper
 
+    def optional(self, f):
+        """Decorator to protect a route with optional authentication.
+
+        This decorator makes authentication for the decorated route optional,
+        meaning that the route is allowed to run with or with
+        authentication given in the request.
+        """
+        async def wrapper(request, *args, **kwargs):
+            auth = self._get_auth(request)
+            if not auth:
+                request.g.current_user = None
+            else:
+                request.g.current_user = await invoke_handler(
+                    self.auth_callback, request, *auth)
+            return await invoke_handler(f, request, *args, **kwargs)
+
+        return wrapper
+
 
 class BasicAuth(BaseAuth):
     """Basic Authentication.

tests/test_auth.py

@@ -45,6 +45,38 @@ class TestAuth(unittest.TestCase):
                 b'foo:baz').decode()}))
         self.assertEqual(res.status_code, 401)
 
+    def test_basic_optional_auth(self):
+        app = Microdot()
+        basic_auth = BasicAuth()
+
+        @basic_auth.authenticate
+        def authenticate(request, username, password):
+            if username == 'foo' and password == 'bar':
+                return {'username': username}
+
+        @app.route('/')
+        @basic_auth.optional
+        def index(request):
+            return request.g.current_user['username'] \
+                if request.g.current_user else ''
+
+        client = TestClient(app)
+        res = self._run(client.get('/'))
+        self.assertEqual(res.status_code, 200)
+        self.assertEqual(res.text, '')
+
+        res = self._run(client.get('/', headers={
+            'Authorization': 'Basic ' + binascii.b2a_base64(
+                b'foo:bar').decode()}))
+        self.assertEqual(res.status_code, 200)
+        self.assertEqual(res.text, 'foo')
+
+        res = self._run(client.get('/', headers={
+            'Authorization': 'Basic ' + binascii.b2a_base64(
+                b'foo:baz').decode()}))
+        self.assertEqual(res.status_code, 200)
+        self.assertEqual(res.text, '')
+
     def test_token_auth(self):
         app = Microdot()
         token_auth = TokenAuth()
@@ -67,7 +99,7 @@ class TestAuth(unittest.TestCase):
             'Authorization': 'Basic foo'}))
         self.assertEqual(res.status_code, 401)
 
-        res = self._run(client.get('/', headers={'Authorization': 'foo'}))
+        res = self._run(client.get('/', headers={'Authorization': 'invalid'}))
         self.assertEqual(res.status_code, 401)
 
         res = self._run(client.get('/', headers={
@@ -75,6 +107,39 @@ class TestAuth(unittest.TestCase):
         self.assertEqual(res.status_code, 200)
         self.assertEqual(res.text, 'user')
 
+    def test_token_optional_auth(self):
+        app = Microdot()
+        token_auth = TokenAuth()
+
+        @token_auth.authenticate
+        def authenticate(request, token):
+            if token == 'foo':
+                return 'user'
+
+        @app.route('/')
+        @token_auth.optional
+        def index(request):
+            return request.g.current_user or ''
+
+        client = TestClient(app)
+        res = self._run(client.get('/'))
+        self.assertEqual(res.status_code, 200)
+        self.assertEqual(res.text, '')
+
+        res = self._run(client.get('/', headers={
+            'Authorization': 'Basic foo'}))
+        self.assertEqual(res.status_code, 200)
+        self.assertEqual(res.text, '')
+
+        res = self._run(client.get('/', headers={'Authorization': 'foo'}))
+        self.assertEqual(res.status_code, 200)
+        self.assertEqual(res.text, '')
+
+        res = self._run(client.get('/', headers={
+            'Authorization': 'Bearer foo'}))
+        self.assertEqual(res.status_code, 200)
+        self.assertEqual(res.text, 'user')
+
     def test_token_auth_custom_header(self):
         app = Microdot()
         token_auth = TokenAuth(header='X-Auth-Token')