diff --git a/tableauserverclient/models/tableau_auth.py b/tableauserverclient/models/tableau_auth.py
index 8cb2a8848..10cf58723 100644
--- a/tableauserverclient/models/tableau_auth.py
+++ b/tableauserverclient/models/tableau_auth.py
@@ -1,16 +1,20 @@
 import abc
+from typing import Dict, Optional
 
 
 class Credentials(abc.ABC):
-    def __init__(self, site_id=None, user_id_to_impersonate=None):
+    def __init__(self, site_id: Optional[str] = None, user_id_to_impersonate: Optional[str] = None) -> None:
         self.site_id = site_id or ""
         self.user_id_to_impersonate = user_id_to_impersonate or None
 
     @property
     @abc.abstractmethod
-    def credentials(self):
-        credentials = "Credentials can be username/password, Personal Access Token, or JWT"
-        +"This method returns values to set as an attribute on the credentials element of the request"
+    def credentials(self) -> Dict[str, str]:
+        credentials = (
+            "Credentials can be username/password, Personal Access Token, or JWT"
+            "This method returns values to set as an attribute on the credentials element of the request"
+        )
+        return {"key": "value"}
 
     @abc.abstractmethod
     def __repr__(self):
@@ -28,7 +32,9 @@ def deprecate_site_attribute():
 
 # The traditional auth type: username/password
 class TableauAuth(Credentials):
-    def __init__(self, username, password, site_id=None, user_id_to_impersonate=None):
+    def __init__(
+        self, username: str, password: str, site_id: Optional[str] = None, user_id_to_impersonate: Optional[str] = None
+    ) -> None:
         super().__init__(site_id, user_id_to_impersonate)
         if password is None:
             raise TabError("Must provide a password when using traditional authentication")
@@ -36,7 +42,7 @@ def __init__(self, username, password, site_id=None, user_id_to_impersonate=None
         self.username = username
 
     @property
-    def credentials(self):
+    def credentials(self) -> Dict[str, str]:
         return {"name": self.username, "password": self.password}
 
     def __repr__(self):
@@ -49,7 +55,13 @@ def __repr__(self):
 
 # A Tableau-generated Personal Access Token
 class PersonalAccessTokenAuth(Credentials):
-    def __init__(self, token_name, personal_access_token, site_id=None, user_id_to_impersonate=None):
+    def __init__(
+        self,
+        token_name: str,
+        personal_access_token: str,
+        site_id: Optional[str] = None,
+        user_id_to_impersonate: Optional[str] = None,
+    ) -> None:
         if personal_access_token is None or token_name is None:
             raise TabError("Must provide a token and token name when using PAT authentication")
         super().__init__(site_id=site_id, user_id_to_impersonate=user_id_to_impersonate)
@@ -57,7 +69,7 @@ def __init__(self, token_name, personal_access_token, site_id=None, user_id_to_i
         self.personal_access_token = personal_access_token
 
     @property
-    def credentials(self):
+    def credentials(self) -> Dict[str, str]:
         return {
             "personalAccessTokenName": self.token_name,
             "personalAccessTokenSecret": self.personal_access_token,
@@ -76,14 +88,14 @@ def __repr__(self):
 
 # A standard JWT generated specifically for Tableau
 class JWTAuth(Credentials):
-    def __init__(self, jwt: str, site_id=None, user_id_to_impersonate=None):
+    def __init__(self, jwt: str, site_id: Optional[str] = None, user_id_to_impersonate: Optional[str] = None) -> None:
         if jwt is None:
             raise TabError("Must provide a JWT token when using JWT authentication")
         super().__init__(site_id, user_id_to_impersonate)
         self.jwt = jwt
 
     @property
-    def credentials(self):
+    def credentials(self) -> Dict[str, str]:
         return {"jwt": self.jwt}
 
     def __repr__(self):