fix(server): improve confusing login errors

[agilgur5]

Fixes #7921, Fixes #12070, Fixes #12168

Motivation

token not valid errors are very confusing for non-operator end users. they also appear before you've even logged in or after you just logged out.

Modifications

fix(ui): don't show auth error when no cookie

• per the in-line comment, this generally means you haven't logged in yet

  • unless you're in SSO auth mode, in which case, you would've had an earlier error
  • or in Server auth mode, in which case, you wouldn't get an error in the first place

• if it's coming from a failed login, instead of saying "Failed to load version/info", say "Login Failed", which is a lot more concrete and understandable at a glance (that doesn't require any knowledge of API endpoints or the code)

• also refactor some code

  • use getCookie func from the previously unused cookie util file
  • standardize the login page to use the setCookie func as well, which effectively duplicated the logic previously
    • name the login func as setUser, which is a lot less confusing than user
  • also make the "authorization" cookie name a shared constant
  • use async/await for all the auth per UI: Refactor to use async/await syntax #11740

fix(server): be more specific about validation errors

• "token not valid" is not the most helpful thing, we can say exactly what's wrong with it

  • which we do for SSO auth errors already

• NOTE: this technically removes the fallback to server auth when using it in conjunction with another one

  • you generally don't want to use server with anything, so that can often be a misconfiguration
    • at my last job, we didn't realize our token was incorrectly formatted until we finally set-up SSO instead of server for the UI (previously we had oauth2-proxy in front)
      • because it was silently falling back to server when client had failed
  • I might change this as it's technically breaking as such, though I think in a good way -- may make that a separate breaking change potentially

Verification

[vlad-ivanov-name]

hello @agilgur5 ,

do you plan to continue working on this PR? do you need any help?

[Joibel]

@vlad-ivanov-name - please feel free to pick this one up and finish it. Please ensure you keep @agilgur5's patches as they are and add on top of them if you're using any of his work, and then the PR get's co-author credits correctly.