Enhance logs

Add remote IP and User-Agent (for HTTP challenge) when error getting
challenge info

config.go

@@ -335,6 +335,7 @@ func (cfg *Config) manageAll(ctx context.Context, domainNames []string, async bo
 			continue
 		}
 
+		// TODO: consider doing this in a goroutine if async, to utilize multiple cores while loading certs
 		// otherwise, begin management immediately
 		err := cfg.manageOne(ctx, domainName, async)
 		if err != nil {

handshake.go

@@ -60,6 +60,7 @@ func (cfg *Config) GetCertificate(clientHello *tls.ClientHelloInfo) (*tls.Certif
 			challengeCert, distributed, err := cfg.getTLSALPNChallengeCert(clientHello)
 			if err != nil {
 				cfg.Logger.Error("tls-alpn challenge",
+					zap.String("remote_addr", clientHello.Conn.RemoteAddr().String()),
 					zap.String("server_name", clientHello.ServerName),
 					zap.Error(err))
 				return nil, err

httphandler.go

@@ -75,6 +75,8 @@ func (am *ACMEIssuer) distributedHTTPChallengeSolver(w http.ResponseWriter, r *h
 	if err != nil {
 		am.Logger.Error("looking up info for HTTP challenge",
 			zap.String("host", host),
+			zap.String("remote_addr", r.RemoteAddr),
+			zap.String("user_agent", r.Header.Get("User-Agent")),
 			zap.Error(err))
 		return false
 	}