Run obtain and refresh token login in a single thread

obtain_and_refresh_token_in_a_single_thread.kt

fun obtainAccessToken(): String {
    val kCriticalSection = DI.get<KCriticalSection>(qualifier = "shared")
    val singleThread = DI.get<CoroutineDispatcher>(qualifier = "shared")

    return runBlocking(singleThread) {
        kCriticalSection.synchronized {
            val accessToken = readAccessTokenFromStorageOrMemory() // might be a suspending call

            if (accessToken != null && System.currentTimeMillis() < accessToken.createdAt + accessToken.expiresIn) {
                return@synchronized accessToken.toString() // access token is valid
            }

            val refreshToken = readRefreshTokenFromSecureStorage() // normally a suspending call

            // normally suspending as it makes another API call
            val newAccessToken = performTokenRefresh(
                accessToken = accessToken,
                refreshToken = refreshToken
            )

            saveAccessTokenToStorageOrMemory(newAccessToken) // might be a suspending call
            return@synchronized newAccessToken.toString()
        }
    }
}