Use debug level logging to avoid performance impact (#23)

[ericlai616]

What is this PR for?

Resolves #23 by logging debug logs at an appropriate logging level to make server less busy for logging during high traffic rate.

Overview or reasons

It appears that current logs in the FIDO server are mainly for debugging purpose, but they are logged in info level.

As a result, even if info level is configured in logback, they are always logged. When traffic rate is high, the server becomes busy for logging.

On the other hand, some logs passes parameters with manual string construction instead of {} placeholder, so the impact is even larger. (See https://www.slf4j.org/faq.html#logging_performance for details)

Tasks

• Align all debugging logs to be debug level: log.info -> log.debug
• Use {} placeholders in log message whenever possible
• Pass objects directly as message parameters instead of manual string construction like toString or String.format. This can avoid redundant computation when the log is not required for the configured log level.
• Prepare Base64url encoded strings for logging and share it in multiple debug logs to avoid redundant encoding.
  • Note that the encoding is still performed no matter what log level is. Since changing log level should have significant improvement, this PR keeps this change minimal.

Result

• The logs are only logged when logback is configured to debug level.

[CLAassistant]

All committers have signed the CLA.

[ericlai616]

Force pushed the same commit with user email linked to CLA.

[kj84park]

Looks good to me. Thank you for your PR!