Automatically derive the kid from the key fingerprint if missing
#4876
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sandhose
approved these changes
Sep 2, 2025
sandhose
changed the title
kid from the key fingerprint if missing
sandhose
added
A-Configuration
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Implements deriving a key’s ID if no explicit
kidis provided. Contains unit tests and documentation.secrets.keys.[].kidcan now be omitted and in this case the kid is automatically derived. If the field is set, the behavior is the same as before.Edit: The derived kid is now the key’s RFC 7638 JWK Thumbprint.
The derived kid is based on a key’s fingerprint: it simply takes the first four bytes and hex-encodes them.For creating the fingerprinting function I took inspiration from how OpenSSH and AWS are doing their key fingerprinting. They take some canonical byte-representation and hash them, but differ in the used hashing function and whether the private key or corresponding public key is used. I ended up using sha256 hashing on the corresponding public key encoded as PSCK#8 DER.