Step 1: Open the "Settings" function on your iPhone, and Click on the "WLAN" button.

Step 2: tap the "Information" icon to check the details of the connected Wi-Fi.

Step 3: Scroll down to the "HTTP PROXY" part, and turn it on.

Step 4: Switch the status to "Manual".

Step 5: Fill in the blanks of "Server" and "Port", switch the button of "Authentication" to the "On" status, and insert "Username" and "Password".