fix(policy): mend an edge case with subrequest auth and query strings

This fixes an unlikely edge case where using subrequest auth and query
strings with path based filtering can cause reality to differ from
administrator intent. This effectively strips the query string from
subrequest auth checks. This deficiency should be fixed in the future.

Ref: AWOO-004
Signed-off-by: Xe Iaso <me@xeiaso.net>

lib/policy/policy_test.go

@@ -1,6 +1,8 @@
 package policy
 
 import (
+	"net/http"
+	"net/http/httptest"
 	"os"
 	"path/filepath"
 	"testing"
@@ -85,3 +87,27 @@ func TestBadConfigs(t *testing.T) {
 		})
 	}
 }
+
+func TestPathCheckerStripsForwardedURIQuery(t *testing.T) {
+	checker, err := NewPathChecker("^/admin$", true)
+	if err != nil {
+		t.Fatal(err)
+	}
+	req := httptest.NewRequest(http.MethodGet, "https://anubis.local/.within.website/x/cmd/anubis/api/check", nil)
+	req.Header.Set("X-Forwarded-Uri", "/admin?x=1")
+	matched, err := checker.Check(req)
+	if err != nil {
+		t.Fatal(err)
+	}
+	if !matched {
+		t.Fatalf("expected exact path checker to match forwarded URI when query string is appended")
+	}
+	req.Header.Set("X-Forwarded-Uri", "/admin")
+	matched, err = checker.Check(req)
+	if err != nil {
+		t.Fatal(err)
+	}
+	if !matched {
+		t.Fatalf("expected exact path checker to match forwarded URI without query string")
+	}
+}