diff --git a/python_ntfy/_ntfy.py b/python_ntfy/_ntfy.py
index bca2d0d..f1c7f73 100644
--- a/python_ntfy/_ntfy.py
+++ b/python_ntfy/_ntfy.py
@@ -46,12 +46,14 @@ def __init__(
         self,
         topic: str,
         server: str = "https://ntfy.sh",
+        auth: tuple[str, str] | str | None = None,
     ) -> None:
         """Itinialize the NtfyClient.
 
         Args:
             topic: The topic to use for this client
             server: The server to connect to. Must include the protocol (http/https)
+            auth: The authentication credentials to use for this client. Takes precedence over environment variables. Can be a tuple of (user, password) or a token.
 
         Returns:
             None
@@ -65,18 +67,39 @@ def __init__(
         self._server = os.environ.get("NTFY_SERVER") or server
         self._topic = topic
         self.__set_url(self._server, topic)
+        self._auth: tuple[str, str] | None = self._resolve_auth(auth)
 
-        # If the user has set the user and password, use that
-        # If the user has set the token, use that
-        # Otherwise, use None
-
-        self._auth: tuple[str, str] | None = None
-        if (user := os.environ.get("NTFY_USER")) and (
-            password := os.environ.get("NTFY_PASSWORD")
-        ):
-            self._auth = (user, password)
-        elif token := os.environ.get("NTFY_TOKEN"):
-            self._auth = ("", token)
+    def _resolve_auth(
+        self, auth: tuple[str, str] | str | None
+    ) -> tuple[str, str] | None:
+        """Resolve the authentication credentials.
+
+        Args:
+            auth: The authentication credentials to use for this client. Takes precedence over environment variables. Can be a tuple of (user, password) or a token string.
+
+        Returns:
+            tuple[str, str] | None: The authentication credentials.
+        """
+        # If the user has supplied credentials, use them (including empty string)
+        if auth is not None:
+            if isinstance(auth, tuple):
+                return auth
+            if isinstance(auth, str):
+                return ("", auth)
+
+        # Otherwise, check environment variables
+        user = os.environ.get("NTFY_USER")
+        password = os.environ.get("NTFY_PASSWORD")
+        token = os.environ.get("NTFY_TOKEN")
+
+        if user and password:
+            return (user, password)
+
+        if token:
+            return ("", token)
+
+        # If no credentials are found, return None
+        return None
 
     def __set_url(
         self,
diff --git a/tests/test_send_message.py b/tests/test_send_message.py
index c797860..c51681d 100644
--- a/tests/test_send_message.py
+++ b/tests/test_send_message.py
@@ -25,7 +25,7 @@ def test_send_without_auth(localhost_server_no_auth, no_auth) -> None:
     assert response["topic"] == topic
 
 
-def test_send_with_auth(localhost_server_auth, user_pass_auth) -> None:
+def test_send_with_auth_env(localhost_server_auth, user_pass_auth) -> None:
     ntfy = NtfyClient(topic=topic)
     response = ntfy.send(message="test_send_with_auth_env")
     print(response)
@@ -33,7 +33,7 @@ def test_send_with_auth(localhost_server_auth, user_pass_auth) -> None:
     assert response["topic"] == topic
 
 
-def test_send_with_auth_token(localhost_server_auth, token_auth) -> None:
+def test_send_with_auth_token_env(localhost_server_auth, token_auth) -> None:
     ntfy = NtfyClient(topic=topic)
     response = ntfy.send(message="test_send_with_auth_token")
     print(response)
@@ -42,6 +42,24 @@ def test_send_with_auth_token(localhost_server_auth, token_auth) -> None:
     assert response["topic"] == topic
 
 
+def test_send_with_auth_args(localhost_server_auth, user_pass_auth) -> None:
+    auth = (environ["NTFY_USER"], environ["NTFY_PASSWORD"])
+    ntfy = NtfyClient(topic=topic, auth=auth)
+    response = ntfy.send(message="test_send_with_auth_args")
+    print(response)
+    assert response["event"] == "message"
+    assert response["topic"] == topic
+
+
+def test_send_with_auth_token_args(localhost_server_auth, token_auth) -> None:
+    auth = environ["NTFY_TOKEN"]
+    ntfy = NtfyClient(topic=topic, auth=auth)
+    response = ntfy.send(message="test_send_with_auth_token_args")
+    print(response)
+    assert response["event"] == "message"
+    assert response["topic"] == topic
+
+
 def test_send_with_markdown(localhost_server_no_auth, no_auth) -> None:
     with Path("tests/assets/test_markdown.md").open() as f:
         message = f.read()