[SIEM] Enrich Privileges endpoint with NP Authentication data

[rylnd]

NP does not currently provide the user's authentication status as a request header. Consequently, I've currently hardcoded the is_authenticated privilege to true. This needs to be replaced with equivalent logic before 7.7 is released.

My understanding is that one can disable the security plugin, disable authentication on elasticsearch, and interact with SIEM in an unauthenticated manner. With that hardcoded value above, they will be perceived as authenticated and things are going to enter undefined behavior.

Per this discussion, the NP work is still ongoing.

What's unclear to me is whether the above situation is going to play well with NP: I suppose it would just be const isAuthenticated = spaces?.isAuthenticated(request) ?? false? We don't seem to support the "optional auth" use case mentioned in the above issue, so that logic seems like it should work.

[elasticmachine]

Pinging @elastic/siem (Team:SIEM)

[rylnd]

Pinging @XavierM since I know you've touched this stuff recently.

[rylnd]

Closed via #61334, backported to 7.7 and 7.x.