wifi username & password in Windows 10

I just had the same problem and I added my network manually.

You need to know your SSID, Security Type and Security Key.

1. Go to Network and Sharing Center.
2. Set up a new connection or network.
3. Manually connect to a wireless network.
4. Enter SSID, security type and key of your wireless network.

http://www.tenforums.com/tutorials/3520-wireless-network-connect-windows-10-a.html

Refer to the suggestions by Santhosh S23 which applies for Windows 10 and check if it helps.

http://answers.microsoft.com/en-us/ie/forum/ie10-windows_7/where-is-my-wifi-user-name-and-password-located/74557205-5103-41d4-943e-865364c7abf5

Go to Start , and select Settings > Network & Internet.

Select the network you want to connect to, and select Connect.

In the search box, enter view network connections, and in the search results, select View network connections.

In Network Connections, press and hold (or right-click) the network name, and select Status > Wireless Properties.

Select the Security tab, and select Show characters.
The password for the wireless network is displayed in the Network security key field.

Hope this helps.