diff --git a/.github/workflows/ci.yml b/.github/workflows/ci.yml
index c298020..1412335 100644
--- a/.github/workflows/ci.yml
+++ b/.github/workflows/ci.yml
@@ -6,7 +6,7 @@ jobs:
   tests:
     strategy:
       matrix:
-        python-version: ['3.8', '3.9', '3.10', '3.11']
+        python-version: ['3.8', '3.9', '3.10', '3.11', '3.12']
         os: [ubuntu]
       fail-fast: true
     runs-on: ${{ matrix.os }}-latest
diff --git a/config/_config.py b/config/_config.py
index ecc0200..872a00f 100644
--- a/config/_config.py
+++ b/config/_config.py
@@ -51,7 +51,7 @@ def merge_list(config: dict) -> None:
                 config.pop(f"{key}[{i}]")
 
 
-def _merge(config: dict):
+def _merge(config: dict) -> None:
     merge_list(config)
     for k, v in config.items():
         merge_list(config[k])
diff --git a/config/auth.py b/config/auth.py
index 9cb5642..55de652 100644
--- a/config/auth.py
+++ b/config/auth.py
@@ -1,3 +1,5 @@
+from typing import Dict
+
 from attrs import field, mutable, validators
 from requests.auth import HTTPBasicAuth
 from requests.exceptions import HTTPError, MissingSchema
@@ -28,7 +30,7 @@ def token(self, value) -> None:
         logger.debug(f"set: [access_token='{self._token}']")
 
     @property
-    def authorization_header(self) -> dict:
+    def authorization_header(self) -> Dict[str, str]:
         return {"Authorization": f"Bearer {self.token}"}
 
     def request_token(self, client_auth: HTTPBasicAuth, data: dict, **kwargs) -> None:
diff --git a/config/spring.py b/config/spring.py
index ea721d6..904a4fd 100644
--- a/config/spring.py
+++ b/config/spring.py
@@ -1,11 +1,10 @@
 """Module for retrieve application's config from Spring Cloud Config."""
 import asyncio
 import os
-from distutils.util import strtobool
 from functools import partial, wraps
 from typing import Any, Callable, Dict, KeysView, Optional, Tuple
 
-from attrs import field, fields_dict, mutable, validators
+from attrs import converters, field, fields_dict, mutable, validators
 from glom import glom
 
 from . import http
@@ -36,10 +35,10 @@ class ConfigClient:
         default=os.getenv("PROFILE", "development"),
         validator=validators.instance_of(str),
     )
-    fail_fast: bool = field(
-        default=bool(strtobool(str(os.getenv("CONFIG_FAIL_FAST", True)))),
+    fail_fast: bool = field(  # type: ignore
+        default=os.getenv("CONFIG_FAIL_FAST", True),
         validator=validators.instance_of(bool),
-        converter=bool,
+        converter=converters.to_bool,
     )
     oauth2: Optional[OAuth2] = field(
         default=None,
@@ -188,7 +187,7 @@ def decrypt(
         return response.text
 
     @property
-    def config(self) -> Dict:
+    def config(self) -> dict:
         """Getter from configurations retrieved from ConfigClient."""
         return self._config
 
diff --git a/setup.cfg b/setup.cfg
index dca35f5..eb9da0c 100644
--- a/setup.cfg
+++ b/setup.cfg
@@ -30,6 +30,7 @@ classifiers =
   Programming Language :: Python :: 3.9
   Programming Language :: Python :: 3.10
   Programming Language :: Python :: 3.11
+  Programming Language :: Python :: 3.12
   Programming Language :: Python :: Implementation :: CPython
   Programming Language :: Python :: Implementation :: PyPy
   Topic :: Software Development :: Libraries
@@ -84,7 +85,7 @@ warn_unused_ignores = True
 warn_unreachable = True
 
 [tox:tox]
-envlist = py{37,38,39,310,311},pypy{3.6,3.7,3.8,3.9,3.10}
+envlist = py{37,38,39,310,311,312},pypy{3.8,3.9,3.10}
 
 [testenv]
 deps = -rrequirements-dev.txt