DingTalkCallbackCrypto

Implements DingTalk's HTTP-callback request verification and optional body decryption for robot message reception. See the DingTalk docs on verifying robot requests and callback body encryption.

Inputs:

• appSecret — the enterprise-internal app secret. Used as the HMAC key for request signature verification: each callback carries timestamp and sign headers, where sign = Base64(HmacSHA256(appSecret, timestamp + "\n" + appSecret)) and the timestamp is a millisecond epoch DingTalk requires to be no older than one hour; timestamps ahead of local time are tolerated only within a clock-skew allowance.

• aesKey — optional 43-character base64 (no padding). When the robot is configured with encryption, the callback body is a {"encrypt": ...} envelope instead of plain JSON, and this key (decoded with an appended "=" to 32 bytes, its first 16 bytes also used as the CBC IV) decrypts it. May be null for robots configured without encryption.

Instances are immutable and thread-safe; #verify and #decrypt may be invoked concurrently from multiple request threads.