If your iPhone is constantly asking you to re-enter passwords every time you want to connect to a WiFi network, then it probably means your Auto Join setting for that particular network is turned off. Fortunately, this is an easy fix. Open the Settings app on your iPhone, then tap WiFi. Select the network you’re having problems with and enable the Auto-Join option. If that doesn’t fix the problem, try resetting that connection. After selecting the network from the WiFi menu, tap Forget This Network then reconnect to it by manually entering the password.