diff --git a/CHANGELOG.md b/CHANGELOG.md
index b437448..d3df921 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -6,6 +6,10 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 
 ## [Unreleased]
 
+## [0.5.0] - 2020-08-19
+### Added
+- Allow to provide an `httpx.Client` instance for `*AuthorizationCode` flows (even `PKCE`), `*ClientCredentials` and `*ResourceOwnerPasswordCredentials` flows.
+
 ## [0.4.0] - 2020-08-07
 ### Changed
 - Mock an access token by default in `httpx_auth.testing.token_cache_mock`. Getting rid of `pyjwt` default dependency for testing.
@@ -43,7 +47,8 @@ Note that a few changes were made:
 ### Added
 - Placeholder for port of requests_auth to httpx
 
-[Unreleased]: https://github.com/Colin-b/httpx_auth/compare/v0.4.0...HEAD
+[Unreleased]: https://github.com/Colin-b/httpx_auth/compare/v0.5.0...HEAD
+[0.5.0]: https://github.com/Colin-b/httpx_auth/compare/v0.4.0...v0.5.0
 [0.4.0]: https://github.com/Colin-b/httpx_auth/compare/v0.3.0...v0.4.0
 [0.3.0]: https://github.com/Colin-b/httpx_auth/compare/v0.2.0...v0.3.0
 [0.2.0]: https://github.com/Colin-b/httpx_auth/compare/v0.1.0...v0.2.0
diff --git a/README.md b/README.md
index f12bdb6..f7f2958 100644
--- a/README.md
+++ b/README.md
@@ -82,6 +82,7 @@ with httpx.Client() as client:
 | `code_field_name`       | Field name containing the code. | Optional | code |
 | `username`              | User name in case basic authentication should be used to retrieve token. | Optional |  |
 | `password`              | User password in case basic authentication should be used to retrieve token. | Optional |  |
+| `client`                | `httpx.Client` instance that will be used to request the token. Use it to provide a custom proxying rule for instance. | Optional |  |
 
 Any other parameter will be put as query parameter in the authorization URL and as body parameters in the token URL.        
 
@@ -133,6 +134,7 @@ with httpx.Client() as client:
 | `failure_display_time`  | In case received token is not valid, this is the maximum amount of milliseconds the failure page will be displayed in your browser. | Optional | 5000 |
 | `header_name`           | Name of the header field used to send token. | Optional | Authorization |
 | `header_value`          | Format used to send the token value. "{token}" must be present as it will be replaced by the actual token. | Optional | Bearer {token} |
+| `client`                | `httpx.Client` instance that will be used to request the token. Use it to provide a custom proxying rule for instance. | Optional |  |
 
 Any other parameter will be put as query parameter in the authorization URL.        
 
@@ -172,6 +174,7 @@ with httpx.Client() as client:
 | `response_type`         | Value of the response_type query parameter if not already provided in authorization URL. | Optional | code |
 | `token_field_name`      | Field name containing the token. | Optional | access_token |
 | `code_field_name`       | Field name containing the code. | Optional | code |
+| `client`                | `httpx.Client` instance that will be used to request the token. Use it to provide a custom proxying rule for instance. | Optional |  |
 
 Any other parameter will be put as query parameter in the authorization URL and as body parameters in the token URL.        
 
@@ -224,6 +227,7 @@ with httpx.Client() as client:
 | `failure_display_time`  | In case received token is not valid, this is the maximum amount of milliseconds the failure page will be displayed in your browser. | Optional | 5000 |
 | `header_name`           | Name of the header field used to send token. | Optional | Authorization |
 | `header_value`          | Format used to send the token value. "{token}" must be present as it will be replaced by the actual token. | Optional | Bearer {token} |
+| `client`                | `httpx.Client` instance that will be used to request the token. Use it to provide a custom proxying rule for instance. | Optional |  |
 
 Any other parameter will be put as query parameter in the authorization URL and as body parameters in the token URL.        
 
@@ -260,6 +264,7 @@ with httpx.Client() as client:
 | `header_value`     | Format used to send the token value. "{token}" must be present as it will be replaced by the actual token. | Optional | Bearer {token} |
 | `scope`            | Scope parameter sent to token URL as body. Can also be a list of scopes. | Optional |  |
 | `token_field_name` | Field name containing the token.             | Optional  | access_token  |
+| `client`           | `httpx.Client` instance that will be used to request the token. Use it to provide a custom proxying rule for instance. | Optional |  |
 
 Any other parameter will be put as body parameter in the token URL.
 
@@ -289,6 +294,7 @@ with httpx.Client() as client:
 | `header_value`     | Format used to send the token value. "{token}" must be present as it will be replaced by the actual token. | Optional | Bearer {token} |
 | `scope`            | Scope parameter sent to token URL as body. Can also be a list of scopes. | Optional |  |
 | `token_field_name` | Field name containing the token.             | Optional  | access_token  |
+| `client`           | `httpx.Client` instance that will be used to request the token. Use it to provide a custom proxying rule for instance. | Optional |  |
 
 Any other parameter will be put as body parameter in the token URL.
 
@@ -327,6 +333,7 @@ with httpx.Client() as client:
 | `header_value`          | Format used to send the token value. "{token}" must be present as it will be replaced by the actual token. | Optional | Bearer {token} |
 | `scope`                 | Scope parameter sent in query. Can also be a list of scopes. | Optional | openid |
 | `token_field_name`      | Field name containing the token. | Optional | access_token |
+| `client`                | `httpx.Client` instance that will be used to request the token. Use it to provide a custom proxying rule for instance. | Optional |  |
 
 Any other parameter will be put as query parameter in the token URL.        
 
diff --git a/httpx_auth/authentication.py b/httpx_auth/authentication.py
index 247cd8b..4eda275 100644
--- a/httpx_auth/authentication.py
+++ b/httpx_auth/authentication.py
@@ -60,14 +60,17 @@ def _get_query_parameter(url: str, param_name: str) -> Optional[str]:
 
 
 def request_new_grant_with_post(
-    url: str, data, grant_name: str, timeout: float, auth=None
+    url: str, data, grant_name: str, client: httpx.Client
 ) -> (str, int):
-    response = httpx.post(url, data=data, timeout=timeout, auth=auth)
-    if response.is_error:
-        # As described in https://tools.ietf.org/html/rfc6749#section-5.2
-        raise InvalidGrantRequest(response)
+    with client:
+        response = client.post(url, data=data)
+
+        if response.is_error:
+            # As described in https://tools.ietf.org/html/rfc6749#section-5.2
+            raise InvalidGrantRequest(response)
+
+        content = response.json()
 
-    content = response.json()
     token = content.get(grant_name)
     if not token:
         raise GrantNotProvided(grant_name, content)
@@ -146,6 +149,8 @@ def __init__(self, token_url: str, username: str, password: str, **kwargs):
         Token will be sent as "Bearer {token}" by default.
         :param scope: Scope parameter sent to token URL as body. Can also be a list of scopes. Not sent by default.
         :param token_field_name: Field name containing the token. access_token by default.
+        :param client: httpx.Client instance that will be used to request the token.
+        Use it to provide a custom proxying rule for instance.
         :param kwargs: all additional authorization parameters that should be put as body parameters in the token URL.
         """
         self.token_url = token_url
@@ -157,22 +162,19 @@ def __init__(self, token_url: str, username: str, password: str, **kwargs):
         self.password = password
         if not self.password:
             raise Exception("Password is mandatory.")
-        self.kwargs = kwargs
 
-        extra_parameters = dict(kwargs)
-        self.header_name = extra_parameters.pop("header_name", None) or "Authorization"
-        self.header_value = (
-            extra_parameters.pop("header_value", None) or "Bearer {token}"
-        )
+        self.header_name = kwargs.pop("header_name", None) or "Authorization"
+        self.header_value = kwargs.pop("header_value", None) or "Bearer {token}"
         if "{token}" not in self.header_value:
             raise Exception("header_value parameter must contains {token}.")
 
-        self.token_field_name = (
-            extra_parameters.pop("token_field_name", None) or "access_token"
-        )
+        self.token_field_name = kwargs.pop("token_field_name", None) or "access_token"
 
         # Time is expressed in seconds
-        self.timeout = int(extra_parameters.pop("timeout", None) or 60)
+        self.timeout = int(kwargs.pop("timeout", None) or 60)
+        self.client = kwargs.pop("client", None) or httpx.Client()
+        self.client.auth = (self.username, self.password)
+        self.client.timeout = self.timeout
 
         # As described in https://tools.ietf.org/html/rfc6749#section-4.3.2
         self.data = {
@@ -180,10 +182,10 @@ def __init__(self, token_url: str, username: str, password: str, **kwargs):
             "username": self.username,
             "password": self.password,
         }
-        scope = extra_parameters.pop("scope", None)
+        scope = kwargs.pop("scope", None)
         if scope:
             self.data["scope"] = " ".join(scope) if isinstance(scope, list) else scope
-        self.data.update(extra_parameters)
+        self.data.update(kwargs)
 
         all_parameters_in_url = _add_parameters(self.token_url, self.data)
         self.state = sha512(all_parameters_in_url.encode("unicode_escape")).hexdigest()
@@ -198,11 +200,7 @@ def auth_flow(
     def request_new_token(self):
         # As described in https://tools.ietf.org/html/rfc6749#section-4.3.3
         token, expires_in = request_new_grant_with_post(
-            self.token_url,
-            self.data,
-            self.token_field_name,
-            self.timeout,
-            auth=(self.username, self.password),
+            self.token_url, self.data, self.token_field_name, self.client
         )
         # Handle both Access and Bearer tokens
         return (self.state, token, expires_in) if expires_in else (self.state, token)
@@ -230,6 +228,8 @@ def __init__(self, token_url: str, client_id: str, client_secret: str, **kwargs)
         Token will be sent as "Bearer {token}" by default.
         :param scope: Scope parameter sent to token URL as body. Can also be a list of scopes. Not sent by default.
         :param token_field_name: Field name containing the token. access_token by default.
+        :param client: httpx.Client instance that will be used to request the token.
+        Use it to provide a custom proxying rule for instance.
         :param kwargs: all additional authorization parameters that should be put as query parameter in the token URL.
         """
         self.token_url = token_url
@@ -241,29 +241,27 @@ def __init__(self, token_url: str, client_id: str, client_secret: str, **kwargs)
         self.client_secret = client_secret
         if not self.client_secret:
             raise Exception("client_secret is mandatory.")
-        self.kwargs = kwargs
 
-        extra_parameters = dict(kwargs)
-        self.header_name = extra_parameters.pop("header_name", None) or "Authorization"
-        self.header_value = (
-            extra_parameters.pop("header_value", None) or "Bearer {token}"
-        )
+        self.header_name = kwargs.pop("header_name", None) or "Authorization"
+        self.header_value = kwargs.pop("header_value", None) or "Bearer {token}"
         if "{token}" not in self.header_value:
             raise Exception("header_value parameter must contains {token}.")
 
-        self.token_field_name = (
-            extra_parameters.pop("token_field_name", None) or "access_token"
-        )
+        self.token_field_name = kwargs.pop("token_field_name", None) or "access_token"
 
         # Time is expressed in seconds
-        self.timeout = int(extra_parameters.pop("timeout", None) or 60)
+        self.timeout = int(kwargs.pop("timeout", None) or 60)
+
+        self.client = kwargs.pop("client", None) or httpx.Client()
+        self.client.auth = (self.client_id, self.client_secret)
+        self.client.timeout = self.timeout
 
         # As described in https://tools.ietf.org/html/rfc6749#section-4.4.2
         self.data = {"grant_type": "client_credentials"}
-        scope = extra_parameters.pop("scope", None)
+        scope = kwargs.pop("scope", None)
         if scope:
             self.data["scope"] = " ".join(scope) if isinstance(scope, list) else scope
-        self.data.update(extra_parameters)
+        self.data.update(kwargs)
 
         all_parameters_in_url = _add_parameters(self.token_url, self.data)
         self.state = sha512(all_parameters_in_url.encode("unicode_escape")).hexdigest()
@@ -278,11 +276,7 @@ def auth_flow(
     def request_new_token(self) -> tuple:
         # As described in https://tools.ietf.org/html/rfc6749#section-4.4.3
         token, expires_in = request_new_grant_with_post(
-            self.token_url,
-            self.data,
-            self.token_field_name,
-            self.timeout,
-            auth=(self.client_id, self.client_secret),
+            self.token_url, self.data, self.token_field_name, self.client
         )
         # Handle both Access and Bearer tokens
         return (self.state, token, expires_in) if expires_in else (self.state, token)
@@ -327,6 +321,8 @@ def __init__(self, authorization_url: str, token_url: str, **kwargs):
         :param code_field_name: Field name containing the code. code by default.
         :param username: User name in case basic authentication should be used to retrieve token.
         :param password: User password in case basic authentication should be used to retrieve token.
+        :param client: httpx.Client instance that will be used to request the token.
+        Use it to provide a custom proxying rule for instance.
         :param kwargs: all additional authorization parameters that should be put as query parameter
         in the authorization URL and as body parameters in the token URL.
         Usual parameters are:
@@ -354,6 +350,9 @@ def __init__(self, authorization_url: str, token_url: str, **kwargs):
         username = kwargs.pop("username", None)
         password = kwargs.pop("password", None)
         self.auth = (username, password) if username and password else None
+        self.client = kwargs.pop("client", None) or httpx.Client()
+        self.client.auth = self.auth
+        self.client.timeout = self.timeout
 
         # As described in https://tools.ietf.org/html/rfc6749#section-4.1.2
         code_field_name = kwargs.pop("code_field_name", "code")
@@ -415,11 +414,7 @@ def request_new_token(self):
         self.token_data["code"] = code
         # As described in https://tools.ietf.org/html/rfc6749#section-4.1.4
         token, expires_in = request_new_grant_with_post(
-            self.token_url,
-            self.token_data,
-            self.token_field_name,
-            self.timeout,
-            auth=self.auth,
+            self.token_url, self.token_data, self.token_field_name, self.client
         )
         # Handle both Access and Bearer tokens
         return (self.state, token, expires_in) if expires_in else (self.state, token)
@@ -462,6 +457,8 @@ def __init__(self, authorization_url: str, token_url: str, **kwargs):
         code by default.
         :param token_field_name: Field name containing the token. access_token by default.
         :param code_field_name: Field name containing the code. code by default.
+        :param client: httpx.Client instance that will be used to request the token.
+        Use it to provide a custom proxying rule for instance.
         :param kwargs: all additional authorization parameters that should be put as query parameter
         in the authorization URL and as body parameters in the token URL.
         Usual parameters are:
@@ -479,6 +476,9 @@ def __init__(self, authorization_url: str, token_url: str, **kwargs):
 
         BrowserAuth.__init__(self, kwargs)
 
+        self.client = kwargs.pop("client", None) or httpx.Client()
+        self.client.timeout = self.timeout
+
         self.header_name = kwargs.pop("header_name", None) or "Authorization"
         self.header_value = kwargs.pop("header_value", None) or "Bearer {token}"
         if "{token}" not in self.header_value:
@@ -560,7 +560,7 @@ def request_new_token(self) -> tuple:
         self.token_data["code"] = code
         # As described in https://tools.ietf.org/html/rfc6749#section-4.1.4
         token, expires_in = request_new_grant_with_post(
-            self.token_url, self.token_data, self.token_field_name, self.timeout
+            self.token_url, self.token_data, self.token_field_name, self.client
         )
         # Handle both Access and Bearer tokens
         return (self.state, token, expires_in) if expires_in else (self.state, token)
@@ -943,6 +943,8 @@ def __init__(self, instance: str, client_id: str, **kwargs):
         :param header_value: Format used to send the token value.
         "{token}" must be present as it will be replaced by the actual token.
         Token will be sent as "Bearer {token}" by default.
+        :param client: httpx.Client instance that will be used to request the token.
+        Use it to provide a custom proxying rule for instance.
         :param kwargs: all additional authorization parameters that should be put as query parameter
         in the authorization URL.
         Usual parameters are:
@@ -997,6 +999,8 @@ def __init__(self, instance: str, client_id: str, **kwargs):
         :param header_value: Format used to send the token value.
         "{token}" must be present as it will be replaced by the actual token.
         Token will be sent as "Bearer {token}" by default.
+        :param client: httpx.Client instance that will be used to request the token.
+        Use it to provide a custom proxying rule for instance.
         :param kwargs: all additional authorization parameters that should be put as query parameter
         in the authorization URL and as body parameters in the token URL.
         Usual parameters are:
@@ -1037,6 +1041,8 @@ def __init__(self, instance: str, client_id: str, client_secret: str, **kwargs):
         :param scope: Scope parameter sent to token URL as body. Can also be a list of scopes.
         Request 'openid' by default.
         :param token_field_name: Field name containing the token. access_token by default.
+        :param client: httpx.Client instance that will be used to request the token.
+        Use it to provide a custom proxying rule for instance.
         :param kwargs: all additional authorization parameters that should be put as query parameter in the token URL.
         """
         authorization_server = kwargs.pop("authorization_server", None) or "default"
diff --git a/httpx_auth/version.py b/httpx_auth/version.py
index 151e68f..c4b9ff7 100644
--- a/httpx_auth/version.py
+++ b/httpx_auth/version.py
@@ -3,4 +3,4 @@
 # Major should be incremented in case there is a breaking change. (eg: 2.5.8 -> 3.0.0)
 # Minor should be incremented in case there is an enhancement. (eg: 2.5.8 -> 2.6.0)
 # Patch should be incremented in case there is a bug fix. (eg: 2.5.8 -> 2.5.9)
-__version__ = "0.4.0"
+__version__ = "0.5.0"
diff --git a/setup.py b/setup.py
index 3ee544f..d27afc4 100644
--- a/setup.py
+++ b/setup.py
@@ -42,7 +42,7 @@
             # Used to generate test tokens
             "pyjwt==1.*",
             # Used to mock httpx
-            "pytest_httpx==0.6.*",
+            "pytest_httpx==0.7.*",
             # Used to check coverage
             "pytest-cov==2.*",
         ]
diff --git a/tests/auth_helper.py b/tests/auth_helper.py
index f301ea0..c82c349 100644
--- a/tests/auth_helper.py
+++ b/tests/auth_helper.py
@@ -5,7 +5,7 @@
 # TODO Remove
 def get_header(httpx_mock: HTTPXMock, auth: httpx.Auth) -> dict:
     # Mock a dummy response
-    httpx_mock.add_response()
+    httpx_mock.add_response(url="http://authorized_only", method="GET")
     # Send a request to this dummy URL with authentication
     response = httpx.get("http://authorized_only", auth=auth)
     # Return headers received on this dummy URL
diff --git a/tests/test_oauth2_authorization_code.py b/tests/test_oauth2_authorization_code.py
index e8d9d81..49e1363 100644
--- a/tests/test_oauth2_authorization_code.py
+++ b/tests/test_oauth2_authorization_code.py
@@ -6,6 +6,40 @@
 from httpx_auth.testing import BrowserMock, browser_mock, token_cache
 
 
+def test_oauth2_authorization_code_flow_uses_provided_client(
+    token_cache, httpx_mock: HTTPXMock, browser_mock: BrowserMock
+):
+    client = httpx.Client(headers={"x-test": "Test value"})
+    auth = httpx_auth.OAuth2AuthorizationCode(
+        "http://provide_code", "http://provide_access_token", client=client
+    )
+    tab = browser_mock.add_response(
+        opened_url="http://provide_code?response_type=code&state=163f0455b3e9cad3ca04254e5a0169553100d3aa0756c7964d897da316a695ffed5b4f46ef305094fd0a88cfe4b55ff257652015e4aa8f87b97513dba440f8de&redirect_uri=http%3A%2F%2Flocalhost%3A5000%2F",
+        reply_url="http://localhost:5000#code=SplxlOBeZQQYbYS6WxSbIA&state=163f0455b3e9cad3ca04254e5a0169553100d3aa0756c7964d897da316a695ffed5b4f46ef305094fd0a88cfe4b55ff257652015e4aa8f87b97513dba440f8de",
+    )
+    httpx_mock.add_response(
+        method="POST",
+        url="http://provide_access_token",
+        json={
+            "access_token": "2YotnFZFEjr1zCsicMWpAA",
+            "token_type": "example",
+            "expires_in": 3600,
+            "refresh_token": "tGzv3JOkF0XG5Qx2TlKWIA",
+            "example_parameter": "example_value",
+        },
+        match_content=b"grant_type=authorization_code&redirect_uri=http%3A%2F%2Flocalhost%3A5000%2F&response_type=code&code=SplxlOBeZQQYbYS6WxSbIA",
+        match_headers={"x-test": "Test value"},
+    )
+    httpx_mock.add_response(
+        match_headers={"Authorization": "Bearer 2YotnFZFEjr1zCsicMWpAA"}
+    )
+    # Send a request to this dummy URL with authentication
+    httpx.get("http://authorized_only", auth=auth)
+    tab.assert_success(
+        "You are now authenticated on 163f0455b3e9cad3ca04254e5a0169553100d3aa0756c7964d897da316a695ffed5b4f46ef305094fd0a88cfe4b55ff257652015e4aa8f87b97513dba440f8de. You may close this tab."
+    )
+
+
 def test_oauth2_authorization_code_flow_get_code_is_sent_in_authorization_header_by_default(
     token_cache, httpx_mock: HTTPXMock, browser_mock: BrowserMock
 ):
diff --git a/tests/test_oauth2_authorization_code_okta.py b/tests/test_oauth2_authorization_code_okta.py
index b1c55a2..c3dfd6b 100644
--- a/tests/test_oauth2_authorization_code_okta.py
+++ b/tests/test_oauth2_authorization_code_okta.py
@@ -7,6 +7,41 @@
 from tests.auth_helper import get_header
 
 
+def test_oauth2_authorization_code_flow_uses_provided_client(
+    token_cache, httpx_mock: HTTPXMock, browser_mock: BrowserMock
+):
+    client = httpx.Client(headers={"x-test": "Test value"})
+    auth = httpx_auth.OktaAuthorizationCode(
+        "testserver.okta-emea.com",
+        "54239d18-c68c-4c47-8bdd-ce71ea1d50cd",
+        client=client,
+    )
+    tab = browser_mock.add_response(
+        opened_url="https://testserver.okta-emea.com/oauth2/default/v1/authorize?client_id=54239d18-c68c-4c47-8bdd-ce71ea1d50cd&scope=openid&response_type=code&state=5264d11c8b268ccf911ce564ca42fd75cea68c4a3c1ec3ac1ab20243891ab7cd5250ad4c2d002017c6e8ac2ba34954293baa5e0e4fd00bb9ffd4a39c45f1960b&redirect_uri=http%3A%2F%2Flocalhost%3A5000%2F",
+        reply_url="http://localhost:5000#code=SplxlOBeZQQYbYS6WxSbIA&state=5264d11c8b268ccf911ce564ca42fd75cea68c4a3c1ec3ac1ab20243891ab7cd5250ad4c2d002017c6e8ac2ba34954293baa5e0e4fd00bb9ffd4a39c45f1960b",
+    )
+    httpx_mock.add_response(
+        method="POST",
+        url="https://testserver.okta-emea.com/oauth2/default/v1/token",
+        json={
+            "access_token": "2YotnFZFEjr1zCsicMWpAA",
+            "token_type": "example",
+            "expires_in": 3600,
+            "refresh_token": "tGzv3JOkF0XG5Qx2TlKWIA",
+            "example_parameter": "example_value",
+        },
+        match_content=b"grant_type=authorization_code&redirect_uri=http%3A%2F%2Flocalhost%3A5000%2F&client_id=54239d18-c68c-4c47-8bdd-ce71ea1d50cd&scope=openid&response_type=code&code=SplxlOBeZQQYbYS6WxSbIA",
+        match_headers={"x-test": "Test value"},
+    )
+    assert (
+        get_header(httpx_mock, auth).get("Authorization")
+        == "Bearer 2YotnFZFEjr1zCsicMWpAA"
+    )
+    tab.assert_success(
+        "You are now authenticated on 5264d11c8b268ccf911ce564ca42fd75cea68c4a3c1ec3ac1ab20243891ab7cd5250ad4c2d002017c6e8ac2ba34954293baa5e0e4fd00bb9ffd4a39c45f1960b. You may close this tab."
+    )
+
+
 def test_oauth2_authorization_code_flow_get_code_is_sent_in_authorization_header_by_default(
     token_cache, httpx_mock: HTTPXMock, browser_mock: BrowserMock
 ):
diff --git a/tests/test_oauth2_authorization_code_pkce.py b/tests/test_oauth2_authorization_code_pkce.py
index 8270d48..32cf16d 100644
--- a/tests/test_oauth2_authorization_code_pkce.py
+++ b/tests/test_oauth2_authorization_code_pkce.py
@@ -7,6 +7,40 @@
 from httpx_auth.testing import BrowserMock, browser_mock, token_cache
 
 
+def test_oauth2_pkce_flow_uses_provided_client(
+    token_cache, httpx_mock: HTTPXMock, monkeypatch, browser_mock: BrowserMock
+):
+    client = httpx.Client(headers={"x-test": "Test value"})
+    monkeypatch.setattr(httpx_auth.authentication.os, "urandom", lambda x: b"1" * 63)
+    auth = httpx_auth.OAuth2AuthorizationCodePKCE(
+        "http://provide_code", "http://provide_access_token", client=client
+    )
+    tab = browser_mock.add_response(
+        opened_url="http://provide_code?response_type=code&state=163f0455b3e9cad3ca04254e5a0169553100d3aa0756c7964d897da316a695ffed5b4f46ef305094fd0a88cfe4b55ff257652015e4aa8f87b97513dba440f8de&redirect_uri=http%3A%2F%2Flocalhost%3A5000%2F&code_challenge=5C_ph_KZ3DstYUc965SiqmKAA-ShvKF4Ut7daKd3fjc&code_challenge_method=S256",
+        reply_url="http://localhost:5000#code=SplxlOBeZQQYbYS6WxSbIA&state=163f0455b3e9cad3ca04254e5a0169553100d3aa0756c7964d897da316a695ffed5b4f46ef305094fd0a88cfe4b55ff257652015e4aa8f87b97513dba440f8de",
+    )
+    httpx_mock.add_response(
+        method="POST",
+        url="http://provide_access_token",
+        json={
+            "access_token": "2YotnFZFEjr1zCsicMWpAA",
+            "token_type": "example",
+            "expires_in": 3600,
+            "refresh_token": "tGzv3JOkF0XG5Qx2TlKWIA",
+            "example_parameter": "example_value",
+        },
+        match_content=b"code_verifier=MTExMTExMTExMTExMTExMTExMTExMTExMTExMTExMTExMTExMTExMTExMTExMTExMTExMTExMTExMTExMTEx&grant_type=authorization_code&redirect_uri=http%3A%2F%2Flocalhost%3A5000%2F&response_type=code&code=SplxlOBeZQQYbYS6WxSbIA",
+        match_headers={"x-test": "Test value"},
+    )
+    assert (
+        get_header(httpx_mock, auth).get("Authorization")
+        == "Bearer 2YotnFZFEjr1zCsicMWpAA"
+    )
+    tab.assert_success(
+        "You are now authenticated on 163f0455b3e9cad3ca04254e5a0169553100d3aa0756c7964d897da316a695ffed5b4f46ef305094fd0a88cfe4b55ff257652015e4aa8f87b97513dba440f8de. You may close this tab."
+    )
+
+
 def test_oauth2_pkce_flow_get_code_is_sent_in_authorization_header_by_default(
     token_cache, httpx_mock: HTTPXMock, monkeypatch, browser_mock: BrowserMock
 ):
diff --git a/tests/test_oauth2_authorization_code_pkce_okta.py b/tests/test_oauth2_authorization_code_pkce_okta.py
index 3e661f9..b4e2c06 100644
--- a/tests/test_oauth2_authorization_code_pkce_okta.py
+++ b/tests/test_oauth2_authorization_code_pkce_okta.py
@@ -7,6 +7,42 @@
 from httpx_auth.testing import BrowserMock, browser_mock, token_cache
 
 
+def test_oauth2_pkce_flow_uses_provided_client(
+    token_cache, httpx_mock: HTTPXMock, monkeypatch, browser_mock: BrowserMock
+):
+    client = httpx.Client(headers={"x-test": "Test value"})
+    monkeypatch.setattr(httpx_auth.authentication.os, "urandom", lambda x: b"1" * 63)
+    auth = httpx_auth.OktaAuthorizationCodePKCE(
+        "testserver.okta-emea.com",
+        "54239d18-c68c-4c47-8bdd-ce71ea1d50cd",
+        client=client,
+    )
+    tab = browser_mock.add_response(
+        opened_url="https://testserver.okta-emea.com/oauth2/default/v1/authorize?client_id=54239d18-c68c-4c47-8bdd-ce71ea1d50cd&scope=openid&response_type=code&state=5264d11c8b268ccf911ce564ca42fd75cea68c4a3c1ec3ac1ab20243891ab7cd5250ad4c2d002017c6e8ac2ba34954293baa5e0e4fd00bb9ffd4a39c45f1960b&redirect_uri=http%3A%2F%2Flocalhost%3A5000%2F&code_challenge=5C_ph_KZ3DstYUc965SiqmKAA-ShvKF4Ut7daKd3fjc&code_challenge_method=S256",
+        reply_url="http://localhost:5000#code=SplxlOBeZQQYbYS6WxSbIA&state=5264d11c8b268ccf911ce564ca42fd75cea68c4a3c1ec3ac1ab20243891ab7cd5250ad4c2d002017c6e8ac2ba34954293baa5e0e4fd00bb9ffd4a39c45f1960b",
+    )
+    httpx_mock.add_response(
+        method="POST",
+        url="https://testserver.okta-emea.com/oauth2/default/v1/token",
+        json={
+            "access_token": "2YotnFZFEjr1zCsicMWpAA",
+            "token_type": "example",
+            "expires_in": 3600,
+            "refresh_token": "tGzv3JOkF0XG5Qx2TlKWIA",
+            "example_parameter": "example_value",
+        },
+        match_content=b"code_verifier=MTExMTExMTExMTExMTExMTExMTExMTExMTExMTExMTExMTExMTExMTExMTExMTExMTExMTExMTExMTExMTEx&grant_type=authorization_code&redirect_uri=http%3A%2F%2Flocalhost%3A5000%2F&client_id=54239d18-c68c-4c47-8bdd-ce71ea1d50cd&scope=openid&response_type=code&code=SplxlOBeZQQYbYS6WxSbIA",
+        match_headers={"x-test": "Test value"},
+    )
+    assert (
+        get_header(httpx_mock, auth).get("Authorization")
+        == "Bearer 2YotnFZFEjr1zCsicMWpAA"
+    )
+    tab.assert_success(
+        "You are now authenticated on 5264d11c8b268ccf911ce564ca42fd75cea68c4a3c1ec3ac1ab20243891ab7cd5250ad4c2d002017c6e8ac2ba34954293baa5e0e4fd00bb9ffd4a39c45f1960b. You may close this tab."
+    )
+
+
 def test_oauth2_pkce_flow_get_code_is_sent_in_authorization_header_by_default(
     token_cache, httpx_mock: HTTPXMock, monkeypatch, browser_mock: BrowserMock
 ):
diff --git a/tests/test_oauth2_client_credential.py b/tests/test_oauth2_client_credential.py
index 70be4b9..a1d6d6d 100644
--- a/tests/test_oauth2_client_credential.py
+++ b/tests/test_oauth2_client_credential.py
@@ -7,6 +7,34 @@
 from httpx_auth.testing import token_cache
 
 
+def test_oauth2_client_credentials_flow_uses_provided_client(
+    token_cache, httpx_mock: HTTPXMock
+):
+    client = httpx.Client(headers={"x-test": "Test value"})
+    auth = httpx_auth.OAuth2ClientCredentials(
+        "http://provide_access_token",
+        client_id="test_user",
+        client_secret="test_pwd",
+        client=client,
+    )
+    httpx_mock.add_response(
+        method="POST",
+        url="http://provide_access_token",
+        json={
+            "access_token": "2YotnFZFEjr1zCsicMWpAA",
+            "token_type": "example",
+            "expires_in": 3600,
+            "refresh_token": "tGzv3JOkF0XG5Qx2TlKWIA",
+            "example_parameter": "example_value",
+        },
+        match_headers={"x-test": "Test value"},
+    )
+    assert (
+        get_header(httpx_mock, auth).get("Authorization")
+        == "Bearer 2YotnFZFEjr1zCsicMWpAA"
+    )
+
+
 def test_oauth2_client_credentials_flow_token_is_sent_in_authorization_header_by_default(
     token_cache, httpx_mock: HTTPXMock
 ):
diff --git a/tests/test_oauth2_client_credential_okta.py b/tests/test_oauth2_client_credential_okta.py
index 94ffed0..98623af 100644
--- a/tests/test_oauth2_client_credential_okta.py
+++ b/tests/test_oauth2_client_credential_okta.py
@@ -1,10 +1,36 @@
 from pytest_httpx import HTTPXMock
+import httpx
 
 import httpx_auth
 from tests.auth_helper import get_header
 from httpx_auth.testing import token_cache
 
 
+def test_okta_client_credentials_flow_uses_provided_client(
+    token_cache, httpx_mock: HTTPXMock
+):
+    client = httpx.Client(headers={"x-test": "Test value"})
+    auth = httpx_auth.OktaClientCredentials(
+        "test_okta", client_id="test_user", client_secret="test_pwd", client=client
+    )
+    httpx_mock.add_response(
+        method="POST",
+        url="https://test_okta/oauth2/default/v1/token",
+        json={
+            "access_token": "2YotnFZFEjr1zCsicMWpAA",
+            "token_type": "example",
+            "expires_in": 3600,
+            "refresh_token": "tGzv3JOkF0XG5Qx2TlKWIA",
+            "example_parameter": "example_value",
+        },
+        match_headers={"x-test": "Test value"},
+    )
+    assert (
+        get_header(httpx_mock, auth).get("Authorization")
+        == "Bearer 2YotnFZFEjr1zCsicMWpAA"
+    )
+
+
 def test_okta_client_credentials_flow_token_is_sent_in_authorization_header_by_default(
     token_cache, httpx_mock: HTTPXMock
 ):
diff --git a/tests/test_oauth2_resource_owner_password.py b/tests/test_oauth2_resource_owner_password.py
index 5fcd869..8bebe72 100644
--- a/tests/test_oauth2_resource_owner_password.py
+++ b/tests/test_oauth2_resource_owner_password.py
@@ -7,6 +7,35 @@
 from httpx_auth.testing import token_cache
 
 
+def test_oauth2_password_credentials_flow_uses_provided_client(
+    token_cache, httpx_mock: HTTPXMock
+):
+    client = httpx.Client(headers={"x-test": "Test value"})
+    auth = httpx_auth.OAuth2ResourceOwnerPasswordCredentials(
+        "http://provide_access_token",
+        username="test_user",
+        password="test_pwd",
+        client=client,
+    )
+    httpx_mock.add_response(
+        method="POST",
+        url="http://provide_access_token",
+        json={
+            "access_token": "2YotnFZFEjr1zCsicMWpAA",
+            "token_type": "example",
+            "expires_in": 3600,
+            "refresh_token": "tGzv3JOkF0XG5Qx2TlKWIA",
+            "example_parameter": "example_value",
+        },
+        match_content=b"grant_type=password&username=test_user&password=test_pwd",
+        match_headers={"x-test": "Test value"},
+    )
+    assert (
+        get_header(httpx_mock, auth).get("Authorization")
+        == "Bearer 2YotnFZFEjr1zCsicMWpAA"
+    )
+
+
 def test_oauth2_password_credentials_flow_token_is_sent_in_authorization_header_by_default(
     token_cache, httpx_mock: HTTPXMock
 ):