Add support for ECC signatures by switching to Crypt::PK::*

[yoe]

There is no Crypt::OpenSSL::* module to support ECC signatures, which the JWT standard specifies. As a result, this module currently does not support ECC tokens, only HMAC and RSA ones.

Switch to Crypt::PK::* instead, which does have a ECC module that has the exact same API as its RSA counterpart.

As an added advantage, Crypt::PK::RSA also supports importing/exporting RSA keys in JWK format, which Crypt::OpenSSL::RSA does not. This might be useful for a module dealing with JSON Web Tokens.

Signed-Off-By: Wouter Verhelst [email protected]