github.com/ureeves/jwt-go-secp256k1 (go): Package secp256k1 implements a jwt.SigningMethod for secp256k1 signatures.  Two different algorithms are implemented: ES256K and ES256K-R. The former produces and verifies using signatures in the R || S format, and the latter in R || S || V. V is the recovery byte, making it possible to recover public keys from signatures.
Keywords: cryptography|golang|jwt|secp256k1