1. Introduction §
This is a short text to introduce you about an OpenBSD feature arrived in 2018 and that may not be known by everyone. Wifi interfaces can have a list of network and their associated passphrase to automatically connect when network is known.
2. How to configure §
The relevant configuration information is in the ifconfig man page, look for "WIRELESS DEVICES" and check the "join" keyword.
Basically, in your /etc/hostname.if file (if being replaced by the interface name like iwm0, athn0 etc...), list every access point you know and their according password.
join android_hotspot wpakey t00345Y4Y0U join my-home wpakey goodbyekitty join friends1 wpakey ilikeb33r5 join favorite-bar-hotspot
This will make the wifi interface to try to connect to the first declared network in the file if multiples access points are available. You can temporarily remove a hotspot from the list using "ifconfig iwm0 -join android_hotspot" if you don't want to connect to it.