Okhttp Authenticator multithreading

Question

I am using OkHttp in my android application with several async requests. All requests require a token to be sent with the header. Sometimes I need to refresh th

Answer 1

This is my solution to make sure to refresh token only once in a multi-threading case, using okhttp3.Authenticator:

class Reauthenticator : Authenticator {

    override fun authenticate(route: Route?, response: Response?): Request? {
        if (response == null) return null
        val originalRequest = response.request()
        if (originalRequest.header("Authorization") != null) return null // Already failed to authenticate
        if (!isTokenValid()) { // Check if token is saved locally
            synchronized(this) {
                if (!isTokenValid()) { // Double check if another thread already saved a token locally
                    val jwt = retrieveToken() // HTTP call to get token
                    saveToken(jwt)
                }
            }
        }
        return originalRequest.newBuilder()
                .header("Authorization", getToken())
                .build()
    }

}

You can even write a unit test for this case, too!