Invalid signature about jsonwebtoken

[waynr]

I've run into a similar issue and have identified the problem as being incompatible signature format.

In the product I am working on I am attempting to validate JWTs whose signatures were produced by google cloud's KMS. In KMS signature verification example doc we can see the doc writers assume a KMS-generated signature would be in ASN1 format:

        // Verify Elliptic Curve signature.
        var parsedSig struct{ R, S *big.Int }
        if _, err = asn1.Unmarshal(signature, &parsedSig); err != nil {
                return fmt.Errorf("asn1.Unmarshal: %w", err)
        }

But jsonwebtoken seems to assume a PKCS#11 style "fixed" signature serialization format

With no way to prefer (when signing) or detect (when verifying) the use of ASN1 for signature serialization.

I'd be willing to submit a PR to address this issue if the maintainer could provide guidance on the preferred approach for enabling the detection or selection of signature serialization format at the public crate api level. I imagine it could be as simple as providing encode_asn1 and decode_asn1 funtions.