[bug] Wunused-private-field with Clang

[Carbenium]

Describe the bug
The following warning is shown during build:

/tmp/cirrus-ci-build/dep/jwt-cpp/include/jwt-cpp/jwt.h:1177:20: warning: private field 'md' is not used [-Wunused-private-field]
                        const EVP_MD* (*md)();

Desktop:

• OS: FreeBSD 12.2
• Compiler clang 10.0.1
• Version 0.5.0 (b45bc99)

[prince-chrismc]

Thanks for reporting the warning, that's always suspicious. 🤔

Typically the md is used to setup the "digest context" but in the case of eddsa it uses

jwt-cpp/include/jwt-cpp/jwt.h

Line 1091 in b45bc99

if (!EVP_DigestSignInit(ctx.get(), nullptr, nullptr, nullptr, pkey.get())) {

and the man pages say

Ed25519 and Ed448
Support no digests (the digest type must be NULL)

This might be some copy paste since they do set it to EVP_sha256