route-proxy: a route carries the policy applied to a request

Implements novox/hq ADR 0108, closing issue 116. The proxy's request path was a host lookup
and a forward, so it applied nothing — while the ingress it replaces relies on four things it
had none of.

Path scoping came first because it is a prerequisite, not a sibling. The table mapped a host
to one target, so a host could not be routed two ways, and the refusal this issue turns on
matches a path on a host already routed to a workload. No amount of authentication or source
filtering would have made it expressible. The table is now host to an ordered list of rules,
matched on path prefix.

The order is total, not just by priority. Sorting on priority alone leaves rules that share
one in whatever order the map produced, so the same declaration would serve differently
between restarts — a fault that works, and works differently each time, which is the hardest
kind to believe when reported. Within a priority the longer path wins, which is also the
intuitive reading.

auth names a secret and never holds one. A declaration carrying a credential is refused
whole rather than served unprotected, so the option ADR 0108 rejected cannot return by
accident. A secret that cannot be read makes the route refuse and say so, rather than serve
the workload unprotected — a gate that cannot check is not a gate that opens, and the
alternative turns a missing file into a silently public admin surface.

Authentication costs one bcrypt comparison on every path including an unknown user, so an
unknown user is not measurably faster than a known one with a wrong password. That difference
is a way to enumerate a route's users from outside it.

Redirects keep the request's own path and query, or canonicalising one name onto another
would land every deep link on the front page and raise no error doing it.

Eleven tests, four of them for the capabilities and two for the failure modes that rot
quietly: the credential-in-a-declaration refusal, and the unreadable secret failing closed.
Nothing else breaks if those stop working, so nothing else would report it.

No new dependency: bcrypt comes from the x/crypto module already required.

examples/route-proxy/routes_test.go

@@ -19,6 +19,23 @@ func write(t *testing.T, body string) string {
 	return path
 }
 
+// plain is the table an ordinary set of routes makes: one host, one target, no policy.
+func plain(routes map[string]string) map[string][]rule {
+	out := map[string][]rule{}
+	for host, target := range routes {
+		out[host] = []rule{{target: target}}
+	}
+	return out
+}
+
+// targetOf is where a host's first matching rule sends a request.
+func targetOf(routes map[string][]rule, host string) string {
+	if rules := routes[host]; len(rules) > 0 {
+		return rules[0].target
+	}
+	return ""
+}
+
 // A route is a grant: the consumer supplies a target, and where that machine is comes from the
 // mesh rather than from a naming convention the proxy has to know.
 func TestARouteGoesToWhereTheMeshSaysTheConsumerIs(t *testing.T) {
@@ -30,7 +47,7 @@ func TestARouteGoesToWhereTheMeshSaysTheConsumerIs(t *testing.T) {
 	}
 	// Lower-cased, because a Host header is not case-sensitive and a route that only answers the
 	// spelling in the manifest answers half the requests made to it.
-	if routes["app.example"] != "http://laptop.internal:8080" {
+	if targetOf(routes, "app.example") != "http://laptop.internal:8080" {
 		t.Fatalf("the route does not point at the consumer: %v", routes)
 	}
 }
@@ -44,7 +61,7 @@ func TestAConsumerOnTheProxysOwnMachineIsReachedOverLoopback(t *testing.T) {
 	if err != nil {
 		t.Fatal(err)
 	}
-	if routes["app.example"] != "http://127.0.0.1:9000" {
+	if targetOf(routes, "app.example") != "http://127.0.0.1:9000" {
 		t.Fatalf("a workload on this machine was not reachable: %v", routes)
 	}
 }
@@ -59,7 +76,7 @@ func TestAContributionMissingWhatARouteNeedsIsSkipped(t *testing.T) {
 	if err != nil {
 		t.Fatal(err)
 	}
-	if len(routes) != 1 || routes["fine.example"] == "" {
+	if len(routes) != 1 || targetOf(routes, "fine.example") == "" {
 		t.Fatalf("an unusable contribution was served: %v", routes)
 	}
 }
@@ -75,7 +92,7 @@ func TestTheProxyReachesTheWorkloadAndNamesWhatItServes(t *testing.T) {
 	host, port, _ := strings.Cut(target, ":")
 
 	held := newTable()
-	held.set(map[string]string{"app.example": "http://" + host + ":" + port})
+	held.set(plain(map[string]string{"app.example": "http://" + host + ":" + port}))
 
 	proxy := httptest.NewServer(handler(held))
 	defer proxy.Close()
@@ -120,16 +137,16 @@ func TestTheProxyReachesTheWorkloadAndNamesWhatItServes(t *testing.T) {
 // nothing fails more visibly than a stale grant, which is exactly why it must not survive.
 func TestWithdrawingARouteStopsServingIt(t *testing.T) {
 	held := newTable()
-	held.set(map[string]string{
+	held.set(plain(map[string]string{
 		"going.example":   "http://a.internal:80",
 		"staying.example": "http://b.internal:80",
-	})
-	held.set(map[string]string{"staying.example": "http://b.internal:80"})
+	}))
+	held.set(plain(map[string]string{"staying.example": "http://b.internal:80"}))
 
-	if _, still := held.find("going.example"); still {
+	if _, still := held.find("going.example", "/"); still {
 		t.Fatal("a route whose module was unassigned is still served")
 	}
-	if _, kept := held.find("staying.example"); !kept {
+	if _, kept := held.find("staying.example", "/"); !kept {
 		t.Fatal("withdrawing one route took another with it")
 	}
 }
@@ -137,8 +154,8 @@ func TestWithdrawingARouteStopsServingIt(t *testing.T) {
 // A Host header carries a port and the name does not.
 func TestARequestNamingAPortStillFindsItsRoute(t *testing.T) {
 	held := newTable()
-	held.set(map[string]string{"app.example": "http://a.internal:8080"})
-	if _, found := held.find("app.example:8080"); !found {
+	held.set(plain(map[string]string{"app.example": "http://a.internal:8080"}))
+	if _, found := held.find("app.example:8080", "/"); !found {
 		t.Fatal("a request to app.example:8080 did not find the route for app.example")
 	}
 }
@@ -168,7 +185,7 @@ func TestTheIssuerIsStagingUnlessNamed(t *testing.T) {
 // rate limit — and the proxy would look healthy throughout.
 func TestNoCertificateIsAskedForOnAnUnroutedName(t *testing.T) {
 	held := newTable()
-	held.set(map[string]string{"photos.example": "http://127.0.0.1:8080"})
+	held.set(plain(map[string]string{"photos.example": "http://127.0.0.1:8080"}))
 	policy := onlyWhatTheMeshSaid(held)
 
 	if err := policy(context.Background(), "photos.example"); err != nil {
@@ -184,7 +201,7 @@ func TestNoCertificateIsAskedForOnAnUnroutedName(t *testing.T) {
 // A route withdrawn stops being certifiable, without the proxy restarting.
 func TestWithdrawingARouteWithdrawsItsCertificate(t *testing.T) {
 	held := newTable()
-	held.set(map[string]string{"photos.example": "http://127.0.0.1:8080"})
+	held.set(plain(map[string]string{"photos.example": "http://127.0.0.1:8080"}))
 	policy := onlyWhatTheMeshSaid(held)
 	if err := policy(context.Background(), "photos.example"); err != nil {
 		t.Fatal(err)