401 error handling when session & token validate in a location block

[shawnhankim]

Background:

• 401 error message shows when session validation and token validation are in a location block.
• So users should be aware of that it is the error for either session or token.

AC:

• Common error message.
• Test w/ 7 IdPs * 2 Flows (Auth Code, PKCE) when $session_validation_enable is set to 1.