Cisco duo encrypting the password in the authproxy config file

 https://help.duo.com/s/article/2340?language=en_US

Backup

Take a backup of your authproxy.cfg file

Make sure your password is stored in secure password manager

Changes
Run a cmd as admin

Switch into the duo folder /bin directory

run 

C:\Program Files\Duo Security Authentication Proxy\bin\authproxy_passwd.exe

Enter the password to be encrypted

The tool will give you output. 

Copy paste that over the password in the authproxy file

You need to change the variable names to x_protected as well

service_account_password

becomes

service_account_password_protected

Restart the service

Test

If all is working make sure your password is stored in pw manager

Delete any plaintext versions of the authproxy file.

If its not working drop the old config back in, restart service and log a call with duo support