CXF STS token caching

A TokenStore instance can be set on any of the STS operations (see AbstractOperation), and it will be used for caching in the token providers, validators, etc. The STS ships with two TokenStore implementations, a DefaultInMemoryTokenStore which just wraps the EHCacheTokenStore discussed above, and an implementation based on HazelCast.

Token caching works in different ways depending on where it is used. Both token providers (SAML and SecurityContextTokens) that ship with the STS cache a successfully generated token. When a SAML or SecurityContextToken (or UsernameToken) is received by the STS for validation, it will first check to see whether the token is stored in the cache. If it is then validation is skipped. If it is not, then the TokenValidator will re-validate the token, and store it in the cache if validation is successful. A slight caveat to this behaviour for SAML Tokens is that token validation is only skipped if the token that is stored in the cache originally was signed, as this signature value is used to check to see if the two SAML Tokens are equal. The TokenCanceller implementation for cancelling SecurityContextTokens in the STS removes the token from the cache, if the token is stored in the cache and proof-of-possession passes.

Finally, two significant changes in CXF 2.6.0 concerning caching in the STS relate to the length of time tokens are valid for. Prior to CXF 2.6.0, SecurityContextTokens and SAML Tokens issued by the STS were valid for a default (configurable) value of 5 minutes. In CXF 2.6.0, both tokens are now issued for a default value of 30 minutes, and are stored in the cache for this length of time as a result.