Add support for auth_time Claim

[chamathns]

Description:
The rule 13 of the ID Token Validation section [1] states,

If the auth_time Claim was requested, either through a specific request for this Claim or by using the max_age parameter, the Client SHOULD check the auth_time Claim value and request re-authentication if it determines too much time has elapsed since the last End-User authentication.

The auth_time claim can be requested in the authentication request sent to the OIDC provider [2] by the OPTIONAL parameter max_age. Or else auth_time can be requested as an Essential Claim. In both of these scenarios, inclusion of auth_time claim in the ID Token is MANDATORY.

Going forward, this claim should be supported since it provides information the client could use to prevent attacks.

[1] - https://openid.net/specs/openid-connect-core-1_0.html#IDTokenValidation
[2] - https://openid.net/specs/openid-connect-core-1_0.html#AuthenticationRequest