Add built-in strategy for brute-force protection

.github/workflows/build.yml

@@ -20,7 +20,7 @@ jobs:
     strategy:
       fail-fast: false
       matrix:
-        python-version: [3.9, "3.10", "3.11", "3.12", "3.13"]
+        python-version: ["3.10", "3.11", "3.12", "3.13", "3.14"]
 
     steps:
       - uses: actions/checkout@v4
@@ -81,18 +81,18 @@ jobs:
 
       - name: Install distribution dependencies
         run: pip install --upgrade build
-        if: matrix.python-version == 3.12
+        if: matrix.python-version == 3.13
 
       - name: Create distribution package
         run: python -m build
-        if: matrix.python-version == 3.12
+        if: matrix.python-version == 3.13
 
       - name: Upload distribution package
         uses: actions/upload-artifact@v4
         with:
           name: dist
           path: dist
-        if: matrix.python-version == 3.12
+        if: matrix.python-version == 3.13
 
   publish:
     runs-on: ubuntu-latest
@@ -105,10 +105,10 @@ jobs:
           name: dist
           path: dist
 
-      - name: Use Python 3.12
+      - name: Use Python 3.13
         uses: actions/setup-python@v3
         with:
-          python-version: "3.12"
+          python-version: "3.13"
 
       - name: Install dependencies
         run: |

.gitignore

@@ -9,3 +9,4 @@ __pycache__
 .mypy_cache
 junit
 coverage.xml
+.local

CHANGELOG.md

@@ -5,6 +5,26 @@ All notable changes to this project will be documented in this file.
 The format is based on [Keep a Changelog](https://keepachangelog.com/en/1.0.0/),
 and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0.html).
 
+## [1.0.4] - 2025-10-18 :beers:
+
+- Add a `guardpost.protection` namespace with classes offering a strategy for
+  brute-force protection against authentication attempts, and to log all failed
+  authentication attempts consistently.
+- Add an `InvalidCredentialsError` exception. `AuthenticationHandler` implementations
+  can raise `InvalidCredentialsError` when invalid credentials are provided, to
+  enable automatic logging and, if enabled, brute-force protection.
+- Add `RateLimiter` class that can block authentication attempts after a configurable
+  threshold is exceeded. By default stores failed attempts in-memory.
+- Integrate `RateLimiter` into `AuthenticationStrategy` with automatic tracking of
+  failed authentication attempts and support for blocking excessive requests.
+- Add Python `3.14` and remove `3.9` from the build matrix.
+- Drop support for Python `3.9` (it reached EOL in October 2025).
+- Add an optional dependency on `essentials`, to use its `Secret` class to handle
+  secrets for JWT validation with symmetric encryption. This is useful to support
+  rotating secrets by updating env variables.
+- Improve exceptions raised for invalid `JWTs` to include the source exception
+  (`exc.__cause__`).
+
 ## [1.0.3] - 2025-10-04 :trident:
 
 - Add a `roles` property to the `Identity` object.

guardpost.code-workspace

@@ -21,7 +21,10 @@
             "editor.rulers": [
                 88,
                 100
-            ]
-        }
+            ],
+            "editor.defaultFormatter": "ms-python.black-formatter"
+        },
+        "python.formatting.provider": "none",
+        "makefile.configureOnOpen": false
     }
 }

guardpost/__about__.py

@@ -1 +1 @@
-__version__ = "1.0.3"
+__version__ = "1.0.4"

guardpost/__init__.py

@@ -11,15 +11,28 @@
     AuthorizationContext,
     AuthorizationError,
     AuthorizationStrategy,
+    ForbiddenError,
     Policy,
     PolicyNotFoundError,
     Requirement,
     RequirementConfType,
     RolesRequirement,
     UnauthorizedError,
 )
+from .errors import (
+    AuthException,
+    InvalidCredentialsError,
+    RateLimitExceededError,
+)
+from .protection import (
+    AuthenticationAttemptsStore,
+    FailedAuthenticationAttempts,
+    InMemoryAuthenticationAttemptsStore,
+    RateLimiter,
+)
 
 __all__ = [
+    "AuthException",
     "AuthenticationHandlerConfType",
     "AuthenticationSchemesNotFound",
     "AuthorizationConfigurationError",
@@ -35,5 +48,12 @@
     "RequirementConfType",
     "RolesRequirement",
     "UnauthorizedError",
+    "ForbiddenError",
     "AuthorizationContext",
+    "RateLimiter",
+    "AuthenticationAttemptsStore",
+    "InMemoryAuthenticationAttemptsStore",
+    "FailedAuthenticationAttempts",
+    "InvalidCredentialsError",
+    "RateLimitExceededError",
 ]

guardpost/authentication.py

@@ -1,11 +1,14 @@
 import inspect
+import logging
 from abc import ABC, abstractmethod
 from functools import lru_cache
+from logging import Logger
 from typing import Any, List, Optional, Sequence, Type, Union
 
 from rodi import ContainerProtocol
 
 from guardpost.abc import BaseStrategy
+from guardpost.protection import InvalidCredentialsError, RateLimiter
 
 
 class Identity:
@@ -108,9 +111,26 @@ def __init__(
         self,
         *handlers: AuthenticationHandlerConfType,
         container: Optional[ContainerProtocol] = None,
+        rate_limiter: Optional[RateLimiter] = None,
+        logger: Optional[Logger] = None,
     ):
+        """
+        Initializes an AuthenticationStrategy instance.
+
+        Args:
+            *handlers: One or more authentication handler instances or types to be used
+                for authentication.
+            container: Optional dependency injection container for resolving handler
+                instances.
+            rate_limiter: Optional RateLimiter to apply rate limiting to authentication
+                attempts.
+            logger: Optional logger instance for logging authentication events. If not
+                provided, defaults to `logging.getLogger("guardpost")`
+        """
         super().__init__(container)
         self.handlers = list(handlers)
+        self._logger = logger or logging.getLogger("guardpost")
+        self._rate_limiter = rate_limiter
 
     def add(self, handler: AuthenticationHandlerConfType) -> "AuthenticationStrategy":
         self.handlers.append(handler)
@@ -151,21 +171,49 @@ async def authenticate(
         self, context: Any, authentication_schemes: Optional[Sequence[str]] = None
     ) -> Optional[Identity]:
         """
-        Tries to obtain the user for a context, applying authentication rules.
+        Tries to obtain the user for a context, applying authentication rules and
+        optional rate limiting.
         """
         if not context:
             raise ValueError("Missing context to evaluate authentication")
 
+        if self._rate_limiter:
+            await self._rate_limiter.validate_authentication_attempt(context)
+
+        identity = None
         for handler in self._get_handlers_by_schemes(authentication_schemes, context):
-            if _is_async_handler(type(handler)):
-                identity = await handler.authenticate(context)  # type: ignore
-            else:
-                identity = handler.authenticate(context)
+            try:
+                identity = await self._authenticate_with_handler(handler, context)
+            except InvalidCredentialsError as invalid_credentials_error:
+                # A client provided credentials of a given type, and they were invalid.
+                # Store the information, so later calls can be validated without
+                # attempting authentication.
+                self._logger.info(
+                    "Invalid credentials received from client IP %s for scheme: %s",
+                    invalid_credentials_error.client_ip,
+                    handler.scheme,
+                )
+                if self._rate_limiter:
+                    await self._rate_limiter.store_authentication_failure(
+                        invalid_credentials_error
+                    )
 
             if identity:
                 try:
                     context.identity = identity
                 except AttributeError:
                     pass
                 return identity
+            else:
+                try:
+                    if context.identity is None:
+                        context.identity = Identity()
+                except AttributeError:
+                    pass
         return None
+
+    async def _authenticate_with_handler(self, handler: AuthenticationHandler, context):
+        if _is_async_handler(type(handler)):
+            return await handler.authenticate(context)  # type: ignore
+        else:
+            return handler.authenticate(context)

guardpost/authorization.py

@@ -7,14 +7,19 @@
 
 from guardpost.abc import BaseStrategy
 from guardpost.authentication import Identity
+from guardpost.errors import AuthException
 
 
-class AuthorizationError(Exception):
-    pass
+class AuthorizationError(AuthException):
+    """
+    Base class for all kinds of AuthorizationErrors.
+    """
 
 
-class AuthorizationConfigurationError(Exception):
-    pass
+class AuthorizationConfigurationError(AuthException):
+    """
+    Exception to describe errors in user-defined authorization configuration.
+    """
 
 
 class PolicyNotFoundError(AuthorizationConfigurationError, RuntimeError):

guardpost/errors.py

@@ -1,6 +1,48 @@
 class AuthException(Exception):
-    """Base class for all exception risen by the library."""
+    """Base class for exceptions raised by GuardPost."""
 
 
 class UnsupportedFeatureError(AuthException):
-    """Exception risen for unsupported features."""
+    """Exception raised for unsupported features."""
+
+
+class InvalidCredentialsError(AuthException):
+    """
+    Exception to be raised when invalid credentials are provided. The purpose of this
+    class is to implement rate limiting and provide protection against brute-force
+    attacks.
+    """
+
+    def __init__(self, client_ip: str, key: str = "") -> None:
+        super().__init__(f"Invalid credentials received from {client_ip}.")
+
+        if not client_ip:
+            raise ValueError("Missing or empty client IP")
+
+        self._client_ip = client_ip
+        self._key = key or client_ip
+
+    @property
+    def client_ip(self) -> str:
+        return self._client_ip
+
+    @property
+    def key(self) -> str:
+        return self._key
+
+    @key.setter
+    def key(self, value: str):
+        self._key = value
+
+
+class RateLimitExceededError(Exception):
+    """
+    Exception raised when too many authentication attempts have been made,
+    triggering rate limiting protection against brute-force attacks.
+    """
+
+    def __init__(self) -> None:
+        super().__init__(
+            "Too many authentication attempts. Access temporarily blocked due to rate "
+            "limiting."
+        )