Messages add iat to id_token

[John Bradley]

Having thought about it a bit more it would be a good practice to have iat issued at time stamp in the token so that clients can detect tokens that were issued a long time ago, but may not have expired. The exp time is likely to be long.

[John Bradley]

re #534 Add iat to id_token.

→ 82f1234eb534

[John Bradley]

Fixes #534 Add iat to id_token.

→ de73bbbe0d12