Re-authenticate a user with X-CSRF-Token
Rasjaad, You can use android account manager https://developer.android.com/reference/android/accounts/AccountManager for this purpose

Here is a sample Drupal 8 Android app code that uses account manager to reauthenticate. https://github.com/onedrupal/One-Drupal-Android

https://github.com/onedrupal/One-Drupal-Android/blob/master/app/src/main/java/com/technikh/onedrupal/activities/ActivityAuthentication.java
At the launch of the activity AccountManager.getAuthTokenByFeatures is called

mAccountManager.getAuthTokenByFeatures(AccountUtils.ACCOUNT_TYPE, AccountUtils.AUTH_TOKEN_TYPE, null, this, null, null, new ActivityAuthentication.GetAuthTokenCallback(), null);


Here is the AccountAuthenticator  https://github.com/onedrupal/One-Drupal-Android/blob/master/app/src/main/java/com/technikh/onedrupal/authenticator/AccountAuthenticator.java

authToken = AccountUtils.mServerAuthenticator.signIn(site_protocol+site_domain, account.name, password);