@davidmorton 
Tried with OBO authentication as per above link you have shared, but still end up with this exception and I see Databricks Free edition at this moment for experimenting.

{"error_code": "BAD_REQUEST", "message": "Encountered an unexpected error while evaluating the model. Verify that the input is compatible with the model for inference. Error 'model_serving_user_credentials auth: Unable to detect credentials for user authorization. This error has two common causes: (1) Improper OBO configuration - ensure you logged your model with a UserAuthPolicy and that the 'Agent Framework: On-Behalf-Of-User Authorization' preview is enabled in your workspace. (2) WorkspaceClient instantiation outside of predict()/predict_stream() - ensure you instantiate the WorkspaceClient inside your predict() or predict_stream() function, not at model-loading time. See https://docs.databricks.com/aws/en/generative-ai/agent-framework/authenticate-on-behalf-of-user for details. If the issue persists, contact Databricks Support.'", "stack_trace": "Traceback (most recent call last):\n File \"/opt/conda/envs/mlflow-env/lib/python3.12/site-packages/databricks/sdk/config.py\", line 691, in init_auth\n self._header_factory = self._credentials_strategy(self)\n ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^\n File \"/opt/conda/envs/mlflow-env/lib/python3.12/site-packages/databricks_ai_bridge/model_serving_obo_credential_strategy.py\", line 181, in __call__\n raise ValueError(\nValueError: Unable to detect credentials for user authorization. This error has two common causes: (1) Improper OBO configuration - ensure you logged your model with a UserAuthPolicy and that the 'Agent Framework: On-Behalf-Of-User Authorization' preview is enabled in your workspace. (2) WorkspaceClient instantiation outside of predict()/predict_stream() - ensure you instantiate the WorkspaceClient inside your predict() or predict_stream() function, not at model-loading time.