Expose TLS placeholders (#2982)

* caddytls: Add CipherSuiteName and ProtocolName functions

The cipher_suites.go file is derived from a commit to the Go master
branch that's slated for Go 1.14.  Once Go 1.14 is released, this file
can be removed.

* caddyhttp: Use commonLogEmptyValue in common_log replacer

* caddyhttp: Add TLS placeholders

* caddytls: update unsupportedProtocols

Don't export unsupportedProtocols and update its godoc to mention that
it's used for logging only.

* caddyhttp: simplify getRegTLSReplacement signature

getRegTLSReplacement should receive a string instead of a pointer.

* caddyhttp: Remove http.request.tls.client.cert replacer

The previous behavior of printing the raw certificate bytes was ported
from Caddy 1, but the usefulness of that approach is suspect.  Remove
the client cert replacer from v2 until a use case is presented.

* caddyhttp: Use tls.CipherSuiteName from Go 1.14

Remove ported version of CipherSuiteName in the process.

1 files changed, 28 insertions, 0 deletions

diff --git a/modules/caddytls/values.go b/modules/caddytls/values.go
index 21a6b33..d231650 100644
--- a/modules/caddytls/values.go
+++ b/modules/caddytls/values.go
@@ -17,6 +17,7 @@ package caddytls
 import (
 	"crypto/tls"
 	"crypto/x509"
+	"fmt"
 
 	"github.com/go-acme/lego/v3/certcrypto"
 	"github.com/klauspost/cpuid"
@@ -127,9 +128,36 @@ var SupportedProtocols = map[string]uint16{
 	"tls1.3": tls.VersionTLS13,
 }
 
+// unsupportedProtocols is a map of unsupported protocols.
+// Used for logging only, not enforcement.
+var unsupportedProtocols = map[string]uint16{
+	"ssl3.0": tls.VersionSSL30,
+	"tls1.0": tls.VersionTLS10,
+	"tls1.1": tls.VersionTLS11,
+}
+
 // publicKeyAlgorithms is the map of supported public key algorithms.
 var publicKeyAlgorithms = map[string]x509.PublicKeyAlgorithm{
 	"rsa":   x509.RSA,
 	"dsa":   x509.DSA,
 	"ecdsa": x509.ECDSA,
 }
+
+// ProtocolName returns the standard name for the passed protocol version ID
+// (e.g.  "TLS1.3") or a fallback representation of the ID value if the version
+// is not supported.
+func ProtocolName(id uint16) string {
+	for k, v := range SupportedProtocols {
+		if v == id {
+			return k
+		}
+	}
+
+	for k, v := range unsupportedProtocols {
+		if v == id {
+			return k
+		}
+	}
+
+	return fmt.Sprintf("0x%04x", id)
+}