Verify at construction that AzureKeyCredentialPolicy receive somethin…

…g it can used (Azure#30380)

* Update _authentication.py

* Feedback

* Black

* Tests

* ChangeLog

sdk/core/azure-core/CHANGELOG.md

@@ -11,6 +11,8 @@
 
 ### Bugs Fixed
 
+- Improve error message when providing the wrong credential type for AzureKeyCredential  #30380
+
 ### Other Changes
 
 ## 1.26.4 (2023-04-06)

sdk/core/azure-core/azure/core/pipeline/policies/_authentication.py

@@ -181,12 +181,14 @@ def __init__(
         prefix: Optional[str] = None,
         **kwargs,  # pylint: disable=unused-argument
     ) -> None:
-        super(AzureKeyCredentialPolicy, self).__init__()
-        self._credential = credential
+        super().__init__()
+        if not hasattr(credential, "key"):
+            raise TypeError("String is not a supported credential input type. Use an instance of AzureKeyCredential.")
         if not name:
             raise ValueError("name can not be None or empty")
         if not isinstance(name, str):
             raise TypeError("name must be a string.")
+        self._credential = credential
         self._name = name
         self._prefix = prefix + " " if prefix else ""
 

sdk/core/azure-core/tests/test_authentication.py

@@ -300,7 +300,7 @@ def verify_authorization_header(request):
 
 
 def test_azure_key_credential_policy_raises():
-    """Tests AzureKeyCredential and AzureKeyCredentialPolicy raises with non-string input parameters."""
+    """Tests AzureKeyCredential and AzureKeyCredentialPolicy raises with non-compliant input parameters."""
     api_key = 1234
     key_header = 5678
     with pytest.raises(TypeError):
@@ -310,6 +310,9 @@ def test_azure_key_credential_policy_raises():
     with pytest.raises(TypeError):
         credential_policy = AzureKeyCredentialPolicy(credential=credential, name=key_header)
 
+    with pytest.raises(TypeError):
+        credential_policy = AzureKeyCredentialPolicy(credential=str(api_key), name=key_header)
+
 
 def test_azure_key_credential_updates():
     """Tests AzureKeyCredential updates"""