header is re-encoded when checking signature/integrity

[Brian Campbell]

Similar to issue #46 but with the header - the input into signing/HMAC and AEAD tag calculation is re-encoding the header value rather than using the original encoded value as is from the message. In practice this should rarely, if ever, be a problem. And it doesn't seem to have been an issue. But it would be more appropriate calculate the signature/tag from the actual encoded message content rather than relying on the encoding to produce the same value from the underlying JSON of the header.

[Brian Campbell]

fix #97 ‘header is re-encoded when checking signature/integrity’ by using the encoded header value as-is from the message as input into singing input

→ <<cset 6f4cf809e381>>

[Brian Campbell]

in v0.5.7