Corrected the spelling of "failed" in the error handling branch of the normalizeString function within smtp/auth_scram.go. This change addresses a minor typographical error to ensure the error message is clear and accurate.
Refactor error return to include more specific information and add a check for TLS connection state in SCRAM-SHA-X-PLUS authentication flow. This ensures clearer error messages and verifies essential prerequisites for secure authentication.
Enhanced code readability and maintainability by adding comprehensive documentation comments to all methods and struct definitions in the `smtp/auth_scram.go` file. This improves clarity on the functionality and usage of the SCRAM (Salted Challenge Response Authentication Mechanism) methods and structures.
Updated method names to more accurately reflect their authentication mechanisms (SCRAM-SHA-1, SCRAM-SHA-1-PLUS, SCRAM-SHA-256, SCRAM-SHA-256-PLUS). Revised corresponding comments to improve clarity and maintain consistency.