There were two major reasons for breaking backwards compatibility with this update. The first was a refactor required to expand the width of the RSA and HMAC-SHA signing implementations. There will likely be no required code changes to support this change.
The second update, while unfortunately requiring a small change in integration, is required to open up this library to other signing methods. Not all keys used for all signing methods have a single standard on-disk representation. Requiring `[]byte` as the type for all keys proved too limiting. Additionally, this implementation allows for pre-parsed tokens to be reused, which might matter in an application that parses a high volume of tokens with a small set of keys. Backwards compatibilty has been maintained for passing `[]byte` to the RSA signing methods, but they will also accept `*rsa.PublicKey` and `*rsa.PrivateKey`.
It is likely the only integration change required here will be to change `func(t *jwt.Token) ([]byte, error)` to `func(t *jwt.Token) (interface{}, error)` when calling `Parse`.
