SWW_APPS: an app's Core Rule Set fixes apply only to the hostnames that serve it (closes #220)

gitea's fixes (its parameters, its cookies and gitea.conf) now apply
only to a hostname SWW_APPS lists gitea for, or to every hostname while
it is unset. Each app's fixes are one .conf file, whose first rule skips
the rest unless Inspect sets tx.app_<name>, and one entry in apps.

A hostname in SWW_APPS that is not a DNS name, such as *.example.com,
stops the start.

Model: opus-5-5

internal/discriminator/coreruleset_test.go

@@ -10,6 +10,7 @@ import (
 	"testing"
 
 	"sneak.berlin/go/smallwebwaf/internal/alerts"
+	"sneak.berlin/go/smallwebwaf/internal/discriminator"
 	"sneak.berlin/go/smallwebwaf/internal/ratelimit"
 	"sneak.berlin/go/smallwebwaf/internal/requestlog"
 )
@@ -21,6 +22,7 @@ const (
 	wafDisabledRules    = "SWW_WAF_DISABLED_RULES"
 	wafExemptPaths      = "SWW_WAF_EXEMPT_PATHS"
 	wafBodyLimit        = "SWW_WAF_BODY_LIMIT"
+	apps                = "SWW_APPS"
 	block               = "block"
 	detect              = "detect"
 )
@@ -237,6 +239,27 @@ func TestDisabledRulesSwitchOffWhatGiteaWouldBeRefused(t *testing.T) {
 	}
 }
 
+func TestGiteasFixesApplyOnlyToAHostnameThatServesGitea(t *testing.T) {
+	t.Parallel()
+
+	// Only gitea's fixes let a file name through in path, a parameter
+	// gitea sends file names in.
+	const fileName = "/?path=.gitignore"
+
+	s := startDiscriminator(t, "", map[string]string{
+		wafMode: block, apps: siteA + ":gitea",
+	})
+
+	wantDisposition(t, do(t, s.question(siteA, client, fileName)),
+		http.StatusOK, discriminator.DispositionAllow)
+	wantDisposition(t, do(t, s.question(siteB, client, fileName)),
+		http.StatusForbidden, discriminator.DispositionDeny)
+
+	lines := s.out.requestLines(t, 2)
+	wantLine(t, lines[0], http.StatusOK, requestlog.ActionForward)
+	wantLine(t, lines[1], http.StatusForbidden, requestlog.ActionWAFBlocked)
+}
+
 func TestAttackInAFormBodyIsRefusedOnlyWhileBodiesAreRead(t *testing.T) {
 	t.Parallel()