It specifies the security mode which the upstream WiFi network adopts. 
See Security Mode for details. 
 
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If the wireless network to be bridged adopts the WEP security mode, Authentication 
Type, Default Key, and Key x (x ranges from 1 to 4) need to be entered manually. 
⚫ 
If the wireless network to be bridged adopts the WPA-PSK, WPA2-PSK, 
WPA-PSK&WPA2-PSK, WPA3-SAE, or WPA2-PSK&WPA3-SAE security mode, 
Encryption Algorithm will be populated automatically and you only need to enter 
the Key.