[ffumero2003]

Context

Several structures that hold credentials print them in toString(): B2AccountAuthorization (authorization token), B2FileSseForRequest (SSE-C customer key), B2WebhookConfiguration (HMAC signing secret), B2WebhookCustomHeader (header values) and B2HeadersImpl (Authorization and X-Bz-Server-Side-Encryption-Customer-Key). Applications that log these objects, or exceptions and debug output that include them, write those values in clear text.

Changes

• toString() replaces the sensitive values with [redacted] (a null value still prints as null). Non-secret fields, including the SSE-C key MD5, are unchanged. B2HeadersImpl matches header names case-insensitively.
• B2EventNotificationRule.COMPARATOR previously ordered rules by the target configuration's toString(). With the redaction, two rules that differ only in a secret would compare equal and one would be dropped from a TreeSet. Webhook targets are now compared field by field (url, custom headers, signing secret, maxEventsPerBatch). Any other target type falls back to toString() ordering, as before, and never throws.
• CHANGELOG.md: an [Unreleased] entry for both behavior changes.

No public API or serialized form changes; JSON output is unaffected.

Verification

Claim	Test
Each structure's toString() omits its secret and keeps non-secret fields	B2AccountAuthorizationTest, B2FileSseForRequestTest, B2WebhookConfigurationTest, B2CustomWebhookHeaderTest, B2HeadersImplTest
Header redaction is case-insensitive	B2HeadersImplTest
Rules differing only in a redacted value stay distinct and both survive in a TreeSet; compareTo is consistent with equals	B2EventNotificationRuleTest
Unknown target configurations are ordered without throwing	B2EventNotificationRuleTest.testCompareToOrdersUnknownTargetConfigurationsWithoutThrowing

Each fix was checked against a deliberate break: restoring the comparator's toString() ordering fails three tests; removing the header redaction fails B2HeadersImplTest; restoring an exception for unknown targets fails 1 of 702 core tests.

$ ./gradlew build
BUILD SUCCESSFUL
54 actionable tasks