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Filtering Logs

Best practice is to prevent logging sensitive data at the source, but that discipline is hard to maintain, especially in a large codebase with many developers. So it's smart to add some filtering at the logger level during initialization.

var sensitiveKeys = []string{"password", "key", "apikey", "secret", "pin", "creditcardno"}

logger := slog.New(slog.NewTextHandler(os.Stdout, &slog.HandlerOptions{
	// Replace any potentially sensitive values with the string [REDACTED]
	ReplaceAttr: func(groups []string, a slog.Attr) slog.Attr {
		if slices.Contains(sensitiveKeys, a.Key) {
			return slog.String(a.Key, "[REDACTED]")
		}
		return a
	},
}))

It's virtually impossible to make this approach 100% thorough. So while it helps as a safety net, treat it as a last resort. Use it, but don't rely on it. The real fix is still to avoid logging sensitive data at the source during implementation and review.

Assignment

Add a last-resort security filter to the logger.

Add a security filter to your replaceAttr function. If a log attribute's key matches a list of sensitive key names (e.g. password, key, apikey, secret, pin, creditcardno), replace its value with [REDACTED]. Use slices.Contains to check the key against your list.
Also check string values for URLs that contain embedded passwords (using url.Parse and URL.User), and redact the password portion if present.
Treat usernames as sensitive in this lesson too by adding the user key to your sensitive-key list.
Make a login request and shorten a URL that contains embedded credentials, then verify both the user field and URL-embedded password are redacted in linko.access.log.

Obviously, you should never ACTUALLY add a password to a log file, even if you know it's being redacted. This is for educational purposes only! No kittens were harmed in the making of this assignment.

Restart your server with LINKO_LOG_FILE=linko.access.log set:

LINKO_LOG_FILE=linko.access.log go run .

After making those requests, check linko.access.log:

user should be [REDACTED]
credentialed URLs should contain a redacted password section (not the real value)

Run and submit the CLI tests from the root of the Linko repo.