`OAuth2TokenProvider` should allow a flexible `systemTime`

[xuanswe]

A global fixed systemTime is not enough to write tests in practice at all.

I propose to change the current implementation

class OAuth2TokenProvider(
        private val keyProvider: KeyProvider = KeyProvider(),
        val systemTime: Instant? = null,
    )

to the backward compatible implemenation like below

typealias TimeProvider = () -> Instant?

class OAuth2TokenProvider(
  private val keyProvider: KeyProvider = KeyProvider(),
  private val timeProvider: TimeProvider,
) {
  val systemTime
    get() = timeProvider()

  @JvmOverloads
  constructor(
    keyProvider: KeyProvider = KeyProvider(),
    systemTime: Instant? = null,
  ) : this(keyProvider, { systemTime })
}

I am not sure if we need to adapt anywhere else (ex. OAuth2TokenProviderDeserializer) with this change or not.

[xuanswe]

@ybelMekk do you agree so that I can contribute a PR?

[xuanswe]

From my understanding, OAuth2TokenProvider is created only in 2 places:

• OAuth2TokenProviderDeserializer

  Here, the purpose is to convert json string into OAuth2TokenProvider object. In this case, we only need static systemTime, so not relevant to the change.

• OAuth2Config

  Here, it could be done programmatically, both static and dynamic systemTime are possible.

[xuanswe]

@ybelMekk PR created :)

[xuanswe]

Hi, could you please review the PR?

[ybelMekk]

Could u please run :formatKotlin and then push the changes?

[xuanswe]

@ybelMekk Thanks for merging and releasing! :)