caddytls: Evict internal certs from cache based on issuer (#6266)v2.8.0-beta.1

* caddytls: Evict internal certs from cache based on issuer

During a config reload, we would keep certs in the cache fi they were used  by the next config. If one config uses InternalIssuer and the other uses a public CA, this behavior is problematic / unintuitive, because there is a big difference between private/public CAs.

This change should ensure that internal issuers are considered when deciding whether to keep or evict from the cache during a reload, by making them distinct from each other and certs from public CAs.

* Make sure new TLS app manages configured certs

* Actually make it work

3 files changed, 51 insertions, 11 deletions

diff --git a/go.mod b/go.mod
index 76a97b1f7..36e2dccd3 100644
--- a/go.mod
+++ b/go.mod
@@ -7,7 +7,7 @@ require (
 	github.com/Masterminds/sprig/v3 v3.2.3
 	github.com/alecthomas/chroma/v2 v2.13.0
 	github.com/aryann/difflib v0.0.0-20210328193216-ff5ff6dc229b
-	github.com/caddyserver/certmagic v0.20.1-0.20240419174353-855d4670a49d
+	github.com/caddyserver/certmagic v0.20.1-0.20240423172519-140a6fa9202e
 	github.com/caddyserver/zerossl v0.1.2
 	github.com/dustin/go-humanize v1.0.1
 	github.com/go-chi/chi/v5 v5.0.12
diff --git a/go.sum b/go.sum
index 8c2fb5686..aad167a2d 100644
--- a/go.sum
+++ b/go.sum
@@ -68,8 +68,8 @@ github.com/aws/smithy-go v1.19.0 h1:KWFKQV80DpP3vJrrA9sVAHQ5gc2z8i4EzrLhLlWXcBM=
 github.com/aws/smithy-go v1.19.0/go.mod h1:NukqUGpCZIILqqiV0NIjeFh24kd/FAa4beRb6nbIUPE=
 github.com/beorn7/perks v1.0.1 h1:VlbKKnNfV8bJzeqoa4cOKqO6bYr3WgKZxO8Z16+hsOM=
 github.com/beorn7/perks v1.0.1/go.mod h1:G2ZrVWU2WbWT9wwq4/hrbKbnv/1ERSJQ0ibhJ6rlkpw=
-github.com/caddyserver/certmagic v0.20.1-0.20240419174353-855d4670a49d h1:fi1dMdHOoyWHXpxpCbaB+H4xdAgQcBP2AXSqpXVpIcg=
-github.com/caddyserver/certmagic v0.20.1-0.20240419174353-855d4670a49d/go.mod h1:e1NhB1rF5KZnAuAX6oSyhE7sg1Ru5bWgggw5RtauhEY=
+github.com/caddyserver/certmagic v0.20.1-0.20240423172519-140a6fa9202e h1:+D6CR2rMrHZe79HSwjgefZWP9y78FMQ2NygXvhF0XVA=
+github.com/caddyserver/certmagic v0.20.1-0.20240423172519-140a6fa9202e/go.mod h1:e1NhB1rF5KZnAuAX6oSyhE7sg1Ru5bWgggw5RtauhEY=
 github.com/caddyserver/zerossl v0.1.2 h1:tlEu1VzWGoqcCpivs9liKAKhfpJWYJkHEMmlxRbVAxE=
 github.com/caddyserver/zerossl v0.1.2/go.mod h1:wtiJEHbdvunr40ZzhXlnIkOB8Xj4eKtBKizCcZitJiQ=
 github.com/cenkalti/backoff/v4 v4.2.1 h1:y4OZtCnogmCPw98Zjyt5a6+QwPLGkiQsYW5oUqylYbM=
diff --git a/modules/caddytls/tls.go b/modules/caddytls/tls.go
index 2a05d5235..14965533e 100644
--- a/modules/caddytls/tls.go
+++ b/modules/caddytls/tls.go
@@ -91,7 +91,8 @@ type TLS struct {
 
 	// set of subjects with managed certificates,
 	// and hashes of manually-loaded certificates
-	managing, loaded map[string]struct{}
+	// (managing's value is an optional issuer key, for distinction)
+	managing, loaded map[string]string
 }
 
 // CaddyModule returns the Caddy module information.
@@ -112,7 +113,7 @@ func (t *TLS) Provision(ctx caddy.Context) error {
 	t.ctx = ctx
 	t.logger = ctx.Logger()
 	repl := caddy.NewReplacer()
-	t.managing, t.loaded = make(map[string]struct{}), make(map[string]struct{})
+	t.managing, t.loaded = make(map[string]string), make(map[string]string)
 
 	// set up a new certificate cache; this (re)loads all certificates
 	cacheOpts := certmagic.CacheOptions{
@@ -266,7 +267,7 @@ func (t *TLS) Provision(ctx caddy.Context) error {
 			if err != nil {
 				return fmt.Errorf("caching unmanaged certificate: %v", err)
 			}
-			t.loaded[hash] = struct{}{}
+			t.loaded[hash] = ""
 		}
 	}
 
@@ -358,10 +359,27 @@ func (t *TLS) Cleanup() error {
 		// compute which certificates were managed or loaded into the cert cache by this
 		// app instance (which is being stopped) that are not managed or loaded by the
 		// new app instance (which just started), and remove them from the cache
-		var noLongerManaged, noLongerLoaded []string
-		for subj := range t.managing {
-			if _, ok := nextTLSApp.managing[subj]; !ok {
-				noLongerManaged = append(noLongerManaged, subj)
+		var noLongerManaged []certmagic.SubjectIssuer
+		var reManage, noLongerLoaded []string
+		for subj, currentIssuerKey := range t.managing {
+			// It's a bit nuanced: managed certs can sometimes be different enough that we have to
+			// swap them out for a different one, even if they are for the same subject/domain.
+			// We consider "private" certs (internal CA/locally-trusted/etc) to be significantly
+			// distinct from "public" certs (production CAs/globally-trusted/etc) because of the
+			// implications when it comes to actual deployments: switching between an internal CA
+			// and a production CA, for example, is quite significant. Switching from one public CA
+			// to another, however, is not, and for our purposes we consider those to be the same.
+			// Anyway, if the next TLS app does not manage a cert for this name at all, definitely
+			// remove it from the cache. But if it does, and it's not the same kind of issuer/CA
+			// as we have, also remove it, so that it can swap it out for the right one.
+			if nextIssuerKey, ok := nextTLSApp.managing[subj]; !ok || nextIssuerKey != currentIssuerKey {
+				// next app is not managing a cert for this domain at all or is using a different issuer, so remove it
+				noLongerManaged = append(noLongerManaged, certmagic.SubjectIssuer{Subject: subj, IssuerKey: currentIssuerKey})
+
+				// then, if the next app is managing a cert for this name, but with a different issuer, re-manage it
+				if ok && nextIssuerKey != currentIssuerKey {
+					reManage = append(reManage, subj)
+				}
 			}
 		}
 		for hash := range t.loaded {
@@ -370,10 +388,19 @@ func (t *TLS) Cleanup() error {
 			}
 		}
 
+		// remove the certs
 		certCacheMu.RLock()
 		certCache.RemoveManaged(noLongerManaged)
 		certCache.Remove(noLongerLoaded)
 		certCacheMu.RUnlock()
+
+		// give the new TLS app a "kick" to manage certs that it is configured for
+		// with its own configuration instead of the one we just evicted
+		if err := nextTLSApp.Manage(reManage); err != nil {
+			t.logger.Error("re-managing unloaded certificates with new config",
+				zap.Strings("subjects", reManage),
+				zap.Error(err))
+		}
 	} else {
 		// no more TLS app running, so delete in-memory cert cache
 		certCache.Stop()
@@ -407,7 +434,20 @@ func (t *TLS) Manage(names []string) error {
 			return fmt.Errorf("automate: manage %v: %v", names, err)
 		}
 		for _, name := range names {
-			t.managing[name] = struct{}{}
+			// certs that are issued solely by our internal issuer are a little bit of
+			// a special case: if you have an initial config that manages example.com
+			// using internal CA, then after testing it you switch to a production CA,
+			// you wouldn't want to keep using the same self-signed cert, obviously;
+			// so we differentiate these by associating the subject with its issuer key;
+			// we do this because CertMagic has no notion of "InternalIssuer" like we
+			// do, so we have to do this logic ourselves
+			var issuerKey string
+			if len(ap.Issuers) == 1 {
+				if intIss, ok := ap.Issuers[0].(*InternalIssuer); ok && intIss != nil {
+					issuerKey = intIss.IssuerKey()
+				}
+			}
+			t.managing[name] = issuerKey
 		}
 	}