At least when using direct grant connect flow [1], the `auth_time` is not present in the decoded_token.
Which fails the conversion to OIDCUser.
The "iat" key is provided though so fallback to use it [2]
Related to T2858
[1] Related to P975
[2] https://github.com/keycloak/keycloak-documentation/blob/master/server_development/topics/action-token-spi.adoc#anatomy-of-action-token