Check existing access token for expiration and refresh if need

token_refresh_logic.kt

suspend fun obtainAccessToken(): String {
    val accessToken = readAccessTokenFromStorageOrMemory() // might be a suspending call
    
    if (accessToken != null && System.currentTimeMillis() < accessToken.createdAt + accessToken.expiresIn) {
        return 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 newAccessToken.toString()
}