Signed-off-by: arekkas <aeneas@ory.am>

This patch adds the (experimental) ability to issue JSON Web Tokens instead of ORY Hydra's opaque access tokens. Please be aware that this feature has had little real-world and unit testing and may not be suitable for production.

Simple integration tests using the JWT strategy have been added to ensure functionality.

To use the new JWT strategy, set environment variable `OAUTH2_ACCESS_TOKEN_STRATEGY` to `jwt`. For example: `export OAUTH2_ACCESS_TOKEN_STRATEGY=jwt`.

Please be aware that we (ORY) do not recommend using the JWT strategy for various reasons. If you can, use the default and recommended "opaque" strategy instead.

Closes #248

Signed-off-by: arekkas <aeneas@ory.am>

Signed-off-by: arekkas <aeneas@ory.am>

This patch introduces more tests for code and refresh flows and the JWT
strategy.

Signed-off-by: arekkas <aeneas@ory.am>