Fixes issue #176. Added VerifiableCredentialJwt to support verifyAndP…

[grahnj]

Refactored VerifiableCredential

Overview

Refactored VerifiableCredential to prevent misuse of parseJwt() which could cause bad actors to submit unverified JWT tokens

Description

Added VerifiableCredentialJwt and a verifyAndParse() function to handle the issues outlined in #176. Additionally, sign() now returns a VerifiableCredentialJwt instead of a String as the only public facing mechanism to enable parseJwt() (via verifyAndPublish()).

How Has This Been Tested?

Existing tests have been refactored to align with these changes. New test class was created (VerifiableCredentialJwtTest) and new test was added to check that verifyAndParse() would work successfully when passed a valid token String. Negative scenarios still test the individual methods directly.

• verifyAndParse verifies and parses valid jwt - Validates that a token is parsed as expected