AuthN: Rebuild Authenticate so we only have to call it once in context handler (#61705)

* API: Add reqSignedIn to router groups

* AuthN: Add fall through in context handler

* AuthN: Add IsAnonymous field

* AuthN: add priority to context aware clients

* ContextHandler: Add comment

* AuthN: Add a simple priority queue

* AuthN: Add Name to client interface

* AuthN: register clients with function

* AuthN: update mock and fake to implement interface

* AuthN: rewrite test without reflection

* AuthN: add comment

* AuthN: fix queue insert

* AuthN: rewrite tests

* AuthN: make the queue generic so we can reuse it for hooks

* ContextHandler: Add fixme for auth headers

* AuthN: remove unused variable

* AuthN: use multierror

* AuthN: write proper tests for queue

* AuthN: Add queue item that can store the value and priority

Co-authored-by: Jo <joao.guerreiro@grafana.com>

pkg/services/authn/authnimpl/priority_queue.go

@@ -0,0 +1,34 @@
+package authnimpl
+
+func newQueue[T any]() *queue[T] {
+	return &queue[T]{items: []queueItem[T]{}}
+}
+
+type queue[T any] struct {
+	items []queueItem[T]
+}
+
+type queueItem[T any] struct {
+	v T
+	p uint
+}
+
+func (q *queue[T]) insert(v T, p uint) {
+	// no items in the queue so we just add it
+	if len(q.items) == 0 {
+		q.items = append(q.items, queueItem[T]{v, p})
+		return
+	}
+
+	// find the position in the queue the item should be placed based on priority
+	for i, item := range q.items {
+		if p < item.p {
+			q.items = append(q.items[:i+1], q.items[i:]...)
+			q.items[i] = queueItem[T]{v, p}
+			return
+		}
+	}
+
+	// item did not have higher priority then what is in the queue currently, so we need to add it to the end
+	q.items = append(q.items, queueItem[T]{v, p})
+}