Auto login for VNC method prompts to input VNC password

Document ID : KB000100261
Last Modified Date : 07/06/2018
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Introduction:
With VNC method, We create a target account, a policy and add the account to VNC access. But We still can't auto login by VNC method. It prompts to input credential to pass VNC authentication.
Question:
Why even created account and policy for VNC access, It still asks to input credential for VNC authentication?
Environment:
It should for all version of PAM
Answer:
This password request is set on VNC server software for security usage. 
It could be disabled under VNC service configuration. 
Use TightVNC as example:
On VNC server side, open configuration by right click VNC software icon at bottom right corner.
Select Server Tab -> unselect option "Require VNC authentication" and Select OK to make it enabled.

But if we disable it, there is no security left at all for connecting to target server via PAM VNC feature, as PAM doesn't support target server credential management via VNC. 
That means if we set VNC access under device of PAM, adding target server account or not under policy doesn't impact connection to destination.