client/web: hook up auth flow

Connects serveTailscaleAuth to the localapi webclient endpoint
and pipes auth URLs and session cookies back to the browser to
redirect users from the frontend.

All behind debug flags for now.

Updates tailscale/corp#14335

Signed-off-by: Sonia Appasamy <sonia@tailscale.com>

client/web/src/hooks/auth.ts

@@ -0,0 +1,37 @@
+import { useCallback, useEffect, useState } from "react"
+import { apiFetch } from "src/api"
+
+export type AuthResponse = {
+  ok: boolean
+  authUrl?: string
+}
+
+// useAuth reports and refreshes Tailscale auth status
+// for the web client.
+export default function useAuth() {
+  const [data, setData] = useState<AuthResponse>()
+  const [loading, setLoading] = useState<boolean>(false)
+
+  const loadAuth = useCallback((wait?: boolean) => {
+    const url = wait ? "/auth?wait=true" : "/auth"
+    setLoading(true)
+    return apiFetch(url, "GET")
+      .then((r) => r.json())
+      .then((d) => {
+        setLoading(false)
+        setData(d)
+      })
+      .catch((error) => {
+        setLoading(false)
+        console.error(error)
+      })
+  }, [])
+
+  useEffect(() => {
+    loadAuth()
+  }, [])
+
+  const waitOnAuth = useCallback(() => loadAuth(true), [])
+
+  return { data, loading, waitOnAuth }
+}