Hello, everyone!
This post describes how to log in to a VM using VNC and the browser displays Authentication failed.
Problem Description
When users login to a VM using VNC, the message "Authentication failed" is displayed.

Problem Analysis
If the authentication fails, it indicates that the password is incorrect.
Generally, this problem does not occur unless the password in the memcache is manually changed or the password is invalid.
Solution
Generally, this problem does not occur. The possible cause is that the bottom-layer password times out. The handling method is as follows: Log in to the VNC again.
If you want to know more information about 'Failed to login VM use VNC' information, please check the summary case: [Fault locate] Failed to Log In to VM Using VNC
That's all, thanks!