Update MCP proxy to adhere to the latest draft of MCP specification

internal/authz/policy.go

@@ -0,0 +1,19 @@
+package authz
+
+import "net/http"
+
+type Decision int
+
+const (
+    DecisionAllow Decision = iota
+    DecisionDeny
+)
+
+type PolicyResult struct {
+    Decision Decision
+    Message  string
+}
+
+type PolicyEngine interface {
+    Evaluate(r *http.Request, claims *TokenClaims, requiredScope string) PolicyResult
+}