Adding "typ" claim to SAD tokens

[Razumain]

A new best practice recommendation for JWT suggests that JWT should include a type taclaration using the "typ" claim. This reduce the risk that one JWT of a particular type is mistaken for a JWT of another type. It is therefore suggested to add a "typ" claim to the SAD JWT, defining it to be a SAD token.

[Razumain]

See section 3.9 of https://tools.ietf.org/html/draft-sheffer-oauth-jwt-bcp-01

[martin-lindstrom]

Solved in PR #30.