enforce dict for credential API input payloads

see: #6363

awx/main/fields.py

@@ -455,6 +455,11 @@ class CredentialInputField(JSONSchemaField):
     def validate(self, value, model_instance):
         # decrypt secret values so we can validate their contents (i.e.,
         # ssh_key_data format)
+
+        if not isinstance(value, dict):
+            return super(CredentialInputField, self).validate(value,
+                                                              model_instance)
+
         decrypted_values = {}
         for k, v in value.items():
             if all([
@@ -466,9 +471,8 @@ class CredentialInputField(JSONSchemaField):
             else:
                 decrypted_values[k] = v
 
-        super(CredentialInputField, self).validate(
-            decrypted_values, model_instance
-        )
+        super(CredentialInputField, self).validate(decrypted_values,
+                                                   model_instance)
 
         errors = []
         inputs = model_instance.credential_type.inputs

awx/main/tests/functional/test_credential.py

@@ -162,7 +162,11 @@ def test_credential_creation(organization_factory):
 
 
 @pytest.mark.django_db
-def test_credential_creation_validation_failure(organization_factory):
+@pytest.mark.parametrize('inputs', [
+    ['must-be-a-dict'],
+    {'user': 'wrong-key'},
+])
+def test_credential_creation_validation_failure(organization_factory, inputs):
     org = organization_factory('test').organization
     type_ = CredentialType(
         kind='cloud',
@@ -180,7 +184,7 @@ def test_credential_creation_validation_failure(organization_factory):
 
     with pytest.raises(ValidationError):
         cred = Credential(credential_type=type_, name="Bob's Credential",
-                          inputs={'user': 'wrong-key'}, organization=org)
+                          inputs=inputs, organization=org)
         cred.save()
         cred.full_clean()