I have an Android 4.1.2 phone, and I need to set a WiFi proxy that requires me to authenticate with a username and password. Where can I setup the user and password for the proxy?
For some one Google may bring you to this post On Android 9, Just do as Harshil mentioned (just provide proxy host name and port, then save), when you using Chrome to access internet, there will be a popup to ask for proxy credential, now you can provide your proxy credential
Long press on that wifi connection, tap on show advanced settings. Fill in your details.
The Google Play store, and Whatsapp won't work. For that you'll have to root your phone, and install Proxy Droid or some such proxy app.