Support for other algorithms (ECDSA, HMAC)

[jwojnowski]

In addition to the RSA algorithms (RS256, RS384, RS512), HMAC-based algorithms (HSxxx) and ECDSA algorithms could also be supported (which OAuth Client Secret used as the key for validating HMAC signature).

I haven't yet seen an OpenID Provider using anything different than RSA, so this is low-priority for now, but if you need this feature, please let me know.