Seeking 5volt DC for auxillary monitoring (via ESP8266 board)

[DBH]

Hello, I have a Caldera Paradise spa w/Watkin controller board (P/N: 1302501-1 rev H).   To monitor temperatures and report wirelessly, I have a prototype board using ESP8266 board requiring 3.3v-5v DC.  I prefer to leverage power source from the watkins board if possible.  Viewing the board it seems to have a few options to supply low voltage DC but I need expert advice on where best to find anywhere from 3.3 to 5v dc.   Options:

1. The watkins board has an peripherals 8 pin port (not connect to anything) with 4.6 vdc on pin 6, but it doesn't power up my ESP8266   not sure why

2. use built-in USB port.. which I would prefer to use, but it seems dead with no power output.  I don't know why... but I assume it needs to be enabled by technicians...

3. use the auxiliary port (unused) but I have no info on it...detailed schematics are hard to find.

Advice?  Options? 

Thanks in advance -- Dave

PS:  I use Home Assistant platform to monitor various home aspects, w/integrations such as the ESP8266 wifi board.

[The_Penguin]

I'm about to do the same, but I don't trust tapping into the low-voltage DC of the controller, so I'm going to tap 120V hot and neutral terminals to a small extension cord (fused at the controller connector) run outside the controller cabinet, then use a small iPhone style USB power supply to power the ESP. 

I know the ESP doesn't draw much current, but I've had enough spa controller issues to last me a while.