Comprehensive and Detailed Explanation:
# HTTP Status Code 401 Unauthorized indicates that authentication credentials were either:
* Missing (e.g., no API key or token).
* Invalid (e.g., expired session, incorrect credentials).
# Error Code Breakdown:# (D) "Unauthorized" (Correct) # Indicates the client must authenticate first.# (A) "Service Unavailable" (503) # Used when the server is down.# (B) "Access Denied" (403) # Used when the client lacks permission even after authentication.# (C) "Not Found" (404) # Used when the resource does not exist.
# Reference: Huawei HCIE Datacom - iMaster NCE-Campus RESTful API Error Codes