Remove iat claim value check

[lbalmaceda]

Changes

According to the spec, checking this value should be optional. Presence check however is not. That remains.

References

https://openid.net/specs/openid-connect-core-1_0.html#IDTokenValidation

The iat Claim can be used to reject tokens that were issued too far away from the current time, limiting the amount of time that nonces need to be stored to prevent attacks. The acceptable range is Client specific.

Testing

• This change adds unit test coverage
• This change adds integration test coverage
• This change has been tested on the latest version of Ruby

Checklist

• I have read the Auth0 general contribution guidelines
• I have read the Auth0 Code of Conduct
• All existing and new tests complete without errors
• Rubocop passes on all added/modified files
• All active GitHub checks have passed