This release includes:

• Support for PSR-16: Common Interface for Caching Libraries cache adapters.
• New NullGrantType for manually specifying an access token without a method for retrieving a new one (see the README for more details).
• The ability to get the RawToken object so you can directly access the OAuth access token and refresh token (if available).
• Fix for incorrect signer interfaces in OAuth2Handler constructor.
• Exclusive lock on token write for thread safety.