**As** an administrator
**I want to** have expiration times of access tokens stored and honored,
**so that** OpenProject does not cause HTTP 401 responses that could've been avoided and cause noise in monitoring and similar services.

**Acceptance criteria**

* When obtaining an `OpenIDConnect::UserToken`, store the expiration date as provided by the OAuth 2.0 token endpoint

* The `UserTokens::FetchService` should take that expiration date into account to judge whether a token is expired

* If the token endpoint does not indicate an expiration time, we assume that the token does not expire Begin of the deletion

* <br>End of the deletion