* Dropped support for `[]byte` keys when using RSA signing methods. This convenience feature could contribute to security vulnerabilities involving mismatched key types with signing methods.
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`.
