Multiple cryptographic issues in Python oic

Impact

• Client implementations using this library

Issues

1. The IdToken signature algorithm was not checked automatically, but only if the expected algorithm was passed in as a kwarg.
2. JWA none algorithm was allowed in all flows.
3. oic.consumer.Consumer.parse_authz returns an unverified IdToken. The verification of the token was left to the discretion of the implementator.
4. iat claim was not checked for sanity (i.e. it could be in the future)

Patches

1. IdToken signature is now always checked.
2. JWA none algorithm is now allowed only if using the response_type code
3. IdToken verification is now done automatically.
4. iat claim is now checked for sanity.