fix(cssc): 31670352 add check for empty token for authentication (1/n)

[cegraybl]

This change is only to add check for empty token.
A following PR will be made to update the oras package. Since there are substantial changes to the client usage.

Adding a centralized check for every token we retrieve from the registry and improve on error logging

[Copilot]

Pull Request Overview

This PR adds an empty token check during authentication and refines error handling in the ACR token retrieval. Key changes include:

• Switching from subprocess.Popen to subprocess.run with improved output handling.
• Inserting a check to detect an empty token and raising a specific error.
• Adjusting the exception handling logic for clearer error messaging.

Comments suppressed due to low confidence (2)

src/acrcssc/azext_acrcssc/helper/_ociartifactoperations.py:157

• [nitpick] Consider using a higher log level (e.g., logger.error) instead of logger.debug when an empty token is detected, as this condition indicates a critical authentication failure.

if not token or token == "":

src/acrcssc/azext_acrcssc/helper/_ociartifactoperations.py:164

• [nitpick] The exception block computes an 'unauthorized' condition but then always raises a generic AzCLIError; consider consolidating the error handling logic to provide a more consistent and clear error message based on the unauthorized case.

unauthorized = (error.stderr

[Ruchii-27]

LGTM