okhttp authenticator cancel request

Question

I'm trying to manage my token expiration with okHttp. So I've read plenty of responses on Internet and they recommand to use okHttp with an Authenticator. So I've created an authenticator :

public class TokenAuthenticator implements Authenticator {

private Context mContext;
private RefreshToken mNewRefreshToken;

public TokenAuthenticator(Context context) {
    this.mContext = context;
}

@Override
public Request authenticate(Route route, final okhttp3.Response response) throws IOException {
    String refreshToken = SharedPreferenceHelper.getSharedPreferenceString(mContext, "refresh_token", null);
    APIService apiService = ServiceGenerator.createAuthenticatedService();
    Call<RefreshToken> call = apiService.refreshToken();
    retrofit2.Response<RefreshToken> responseCall = call.execute();

    // If success, we saved new token to SharedPref and redo a request to the server with new token
    if (responseCall.code() == 200) {
        mNewRefreshToken = responseCall.body();
        SharedPreferenceHelper.setSharedPreferenceString(mContext, "refresh_token", mNewRefreshToken.getRefreshToken());
        SharedPreferenceHelper.setSharedPreferenceString(mContext, "access_token", mNewRefreshToken.getAccessToken());
        return response.request().newBuilder()
                .header("Authorization", "Bearer " + mNewRefreshToken.getAccessToken())
                .build();
    }

    // If refreshToken expired, we logout
    if (responseCall.code() == 401) {
        //todo
        return null;
    }

    return null;
}
}

The problem is even If I return null, it will do a new request again, even if the request is not valid. I want to cancel the request but I haven't find anything about it. Does someone have an idea ?

Thanks you