Design API authentication mechanisms with consistent patterns, clear documentation, and helpful error messages. When implementing authentication: 1. **Document authentication requirements explicitly**: - Specify expected username/token formats and any special cases - Explain how authentication failures are handled 2. **Design credentials lookup intelligently**: ```python # Prefer using the base index URL for credential lookup # Instead of: credentials = keyring.get_credential(package_url, None) # Use: credentials = keyring.get_credential(index_url, None) ``` 3. **Provide clear error messages for authentication failures**: ``` If you use `--token "$JFROG_TOKEN"` with JFrog, you will receive a 401 Unauthorized error as JFrog requires an empty username but uv passes `__token__` as the username when `--token` is used. ``` 4. **Consider consistency across similar operations**: - Use the same authentication patterns for related endpoints - Document when different operations require different authentication formats - Be explicit about URL formatting requirements (e.g., trailing slashes) 5. **Test authentication edge cases**: - Verify behavior with missing credentials - Test various token formats - Confirm proper handling of authentication failures